What is a common phrase to describe something that changes while you are working on it without your being aware of it.

For example: you are adding comments to a document, and when you submit them you see that the doc was completely changed in the meantime and your comments are not relevant.

  • 2
    An adjective could be evolving. But you are looking for a phrase, aren't you?
    – edmz
    Commented Jul 27, 2015 at 9:47
  • 4
    It's like playing Whack-a-Mole.
    – Hot Licks
    Commented Jul 27, 2015 at 13:34
  • 9
    In software we call that thing a requirement haha. They always change when you are working on one. Commented Jul 27, 2015 at 16:22
  • 1
    also known as "race condition" but not so common
    – Joshua
    Commented Jul 27, 2015 at 20:34
  • 2
    "Software." ... Commented Jul 28, 2015 at 7:04

27 Answers 27


I would suggest moving target. Longman online (3) says:

a moving target something that is changing continuously, so that it is very difficult to criticize it or compete against it

  • 3
    This is good, but I would extend the analogy to the full "shooting at a moving target". I think it's better imagery that way.
    – Dan
    Commented Jul 28, 2015 at 0:04
  • 1
    This is pretty good, but when one is shooting at a target one is usually looking at it the whole time. The OP's situation seems to emphasize that the 'motion' of the target is unknown until after one's efforts have reached a pause or a conclusion.
    – hBy2Py
    Commented Jul 29, 2015 at 2:49
  • 1
    @brian - It's just a metaphor. Not to be analyzed too closely or taken literally.
    – Jim Mack
    Commented Jul 29, 2015 at 2:53
  • Oops, I should've made that @Dan -- the plain moving target is definitely better.
    – hBy2Py
    Commented Jul 29, 2015 at 2:56

'Capricious' sounds like more close since its more close to being 'arbitrary'.

'Volatile' is also nice to use here but if it is regarding your example of a document it must be 'Dynamic'

  • 6
    I like volatile because it implies a negative property of it being so: making comments on a document that was changed making them moot, that's working on a volatile document. Commented Jul 27, 2015 at 11:29
  • 6
    Volatile would be my answer.
    – Avon
    Commented Jul 27, 2015 at 11:31

If you're looking for one with a negative connotation - you can say you are "building on quicksand".


In the UK we often accuse someone of "moving the goal posts" if they change requirements or conditions in a way that makes our efforts or arguments redundant. The same phrase can also be used in a less accusatory manner if events overtake us, but this is slightly less common, IME.


I would use "dynamic" which google defines as

(of a process or system) characterized by constant change, activity, or progress

If you wish to use it as a phrase then try "dynamic system", "dynamic process", "the dynamic nature of..." or "dynamic in nature"

  • I don't believe Google gave that definition; it merely displayed one given by a specific website.
    – Joachim
    Commented Sep 12, 2022 at 22:40

"in flux" or "ephemeral" both seem useful here.


I've heard this situation called shifting requirements.

"It's hard to predict what the final product will look like, thanks to all these shifting requirements!"


We always called it a living document. Changes are ever happening and the status quo is always in flux.


The 1st word that comes to mind is "mercurial"- defined as changeable; volatile; fickle; flighty; erratic: Other fine words I would use would also be things like protean or mutable

If we are talking about something changing because you are working on it there are some good science terms namely the "Uncertainty principle", that observation alters the outcome. Alternately it could also be said to be "Schrodinger's Cat" a thought experiment where the item changes at the moment you observe it.

  • 1
    Actually in Schrodinger's thought experiment the item does not change. Schrodinger said that even though the outcome was not observed, whether it was observed or not wasn't important. Simply a restatement of "if a tree falls in the woods..." Commented Jul 29, 2015 at 20:58
  • I have always preferred the Many Worlds Interpretation so both realities exist at all times we are just unclear which reality we are in until it is observed. Further more whether or not an observation is made is also uncertain until it is observed, infinitum. Still, while it is not a perfect fit I do believe it fills the need presented as a piece of figurative language.
    – Yeshe
    Commented Jul 30, 2015 at 1:35
  • But that was not Schrodinger's intent and not even a valid restatement of the many worlds hypothesis. Commented Jul 30, 2015 at 12:26

Evolving could be a suitable option.


“We Are Building a Plane in Mid-Air”


I'm not sure if this is a purely Australian expression, but here we often say that the "goalposts are shifting" in a situation where you can't achieve anything due to constantly changing requirements.

  • As a native U.S. speaker I've never heard this but it makes sense Commented Jul 29, 2015 at 13:22

The phrase I would use in this case is "... right out from under me," with the leading part variable depending on the context. In your particular example, I would say something like:

Well, nuts, looks like this document got revised right out from under me.


Fluid (reference.com)

changing readily; shifting; not fixed, stable, or rigid:

Fluid (free dictionary)

fluid - subject to change; variable; "a fluid situation fraught with uncertainty"; "everything was unstable following the coup"


liable to change or fluctuate quickly: an unstable weather pattern.

(an unstable work/code/dev environment)


Posts submitted to StackExchange are subject to change and are continually evolving due to the editorial efforts of the community. That is the nature of the beast here at SE.

  • 1
    The nature of the beast isn't really relevant. The other two fit pretty well, I'd say.
    – Dan
    Commented Jul 28, 2015 at 0:03
  • I thought about adding that, that last one explicitly relies on context.
    – Mazura
    Commented Jul 28, 2015 at 0:21

I have yet to see someone mention the most common phrase I would use to describe this: a ninja edit; that is, a change to something that happens while you are commenting on it.

I find it to be a very common saying on forums and message boards. Urban dictionary confirms this, if you consider that valid:

A ninja edit is an change made to a published post or article (typically on a bulletin board) that preempts the first response made.


'The ground is shifting under my feet' is an expression that I think most closely reflects the situation described of a document being edited while you are editing it.

'Shifting goalposts' is not quite analogous. More suitable for the 'boss' changing what they want the document to say when you present it for review.


Try quicksilver. It has the element of mercurial (being a colloquialism for the element mercury) but also contains the uncertainty principle idea as it "runs away" when you try to touch it.

So, you could say "editing quicksilver" or "a quicksilver task" or "the quicksilver meaning" or "a page of quicksilver paragraphs".

It also has a kind of infinite regression quality, since it was originally the name of the mercury / tin alloy used on the backs of mirrors to cause reflection.


How about transitory, fleeting, or fugacious?

  • Welcome to EL&U. Answers at StackExchange are expected to be definitive; I encourage you to edit your post to explain why you would suggest these words, including appropriate examples, dictionary definitions, or other appropriate references. I encourage you to take the site tour and review the help center for additional guidance.
    – choster
    Commented Jul 29, 2015 at 14:57
  • Interesting. I'm wondering why you singled out my post when nearly all the other posters have simply provided their suggestions without explanations. A simple dictionary lookup should reveal why these choices were selected. Commented Jul 29, 2015 at 15:21
  • I commented on yours because someone flagged yours and it appeared in my review queue; I am not trying to single you out. And no, a "simple dictionary lookup" is rarely sufficient, because words have multiple meanings and are not always interchangeable in context.
    – choster
    Commented Jul 29, 2015 at 15:30
  • In that case, I'm employing the Oxford English Dictionary's usage. Commented Jul 29, 2015 at 15:43

You might consider evolving, mutating or mutable.


Some additional phases that I have heard in the past include:

Dancing on shifting sands
Running on water
Snatching at fog
Trying to nail down a shadow

It has an unstable base

is the phrase that comes to my mind.


The phrase which springs to mind for this to me is "Scope Creep":


A few phrases that capture the time / out-of-step component of your question: "a day late and a dollar short" or "always behind the eight-ball" or "I zig when everyone else zags.

  • Please edit your answer to explain why this phrase is a good answer. Commented Aug 5, 2015 at 8:50

You can probably say, by the minute, transient, on the turn. Since you asked for a phrase the first and last should do.




like nailing jelly to a tree

  • You can also nail jelly to the wall. Commented Jul 28, 2015 at 14:41
  • Answers are better when they define the words or phrases that they say are good fits. For example, I would say "nailing jelly to a tree" is a Sisyphean task, more than one related to change. Commented Jul 30, 2015 at 10:04

I'd say : Feels like working on a chameleon.

  • 3
    Can you show any evidence that this is common? Commented Jul 28, 2015 at 13:46
  • Your suggestion is quite evocative, but I have to agree with curiousdannii that it doesn't meet the questioner's criterion of being a common phrase in English.
    – Sven Yargs
    Commented Jul 28, 2015 at 18:40

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