A word to describe things that reduce control

Question

I'm writing about the concept of "that which has a chance of preventing the intended or desired result". I refer to it frequently and it's very inconvenient to define it every time so I need to find a phrase or (preferably) single word to use as a label for it.

I've considered terms like "obstacle" or "challenge" but some obstacles can be reliably overcome and the word challenge implies that skill is a factor. So far I've used the word "uncertainty" but I think it's too extensive as it applies to things that have no bearing on the intended or desired result.

Is there a word or phrase to describe that which reduces control or produces the opposite of control?

Edit: I need to use the word consistently in several sentences. So let me give you a paragraph instead: "When a users interact with software there are always X. If you're designing a software tool you want to minimize X to provide the user a reliable tool. But if you're making a game you need X to make it exciting for the player."

If you replace X with "things that which have a chance of preventing the intended or desired result" you get the correct meaning but the sentence becomes incredibly awkward. It's hard to find a word/phrase with a good match since it's so precise. If there's no word like that I'll use the closest thing.

Answer 1

I'd suggest unpredictability. Unpredictability is not good for non-gaming software, but it is desirable while creating gaming software.

Unpredictability _{Oxford Dictionary}

Meaning: Inability to be predicted; changeability

Usage: "the constant element of unpredictability keeps the show fresh."

Your paragraph:

"When a users interact with software there are always unpredictability. If you're designing a software tool you want to minimize unpredictability to provide the user a reliable tool. But if you're making a game you need unpredictability to make it exciting for the player."

Answer 2

It sounds like you're talking about a level of randomness. The technical term is noise. It hinders control and introduces a measure of unpredictability.

noise noun 2.1 Random fluctuations that obscure or do not contain meaningful data or other information. ‘over half the magnitude of the differences came from noise in the data’ - ODO

In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of an expected signal. - wikipedia; emphasis, mine

Answer 3

"Difficulty" might fit.

It's defined in OLO as state of being difficult or something that is difficult.

Difficult
1.Needing much effort or skill to accomplish, deal with, or understand.
1.1 Characterized by or causing hardships or problems.
Oxford Living Dictionaries

It seems to match your need when you say:

things that which have a chance of preventing the intended or desired result

Filling the blanks of your example sentence results in the following:

"When a users interact with software there are always [difficulties]. If you're designing a software tool you want to minimize [difficulties] to provide the user a reliable tool. But if you're making a game you need [difficulty] to make it exciting for the player."