Does there exist a single word, either an adjective or a noun, that effectively describes an individual who habitually underestimates things—e.g., cost, time required, complexity?
- Anybody can ask a question
- Anybody can answer
- The best answers are voted up and rise to the top
How about an optimist:
If you really and truly want to make do with just a single word alone, you are going to have to go with a word like a chronic underestimater or underestimator, a misjudger or even a low-baller.
So it seems that they are perpetually falling short of the mark in their subaccurate assessments. Given that, I think what you are really looking for is someone who is actually overestimating not underestimating something. They are overestimating their own abilities at getting things done.
When this is a chronic characteristic, what you have here is someone subject to the Dunning–Kruger effect:
Someone who is actually competent will learn from their previous mistakes, and make allowances for all this in the future. But those of lesser competence are also less competent at assessing their own competence, and so always think they will do more in less time — and do a better job at it, too.
So I suppose you could them a victim of the Dunning-Kruger effect, or just a Dunning-Krugerite for short. I know I’ve certainly used the term with people whom I know are certain to understand me, but it is not in common parlance.
Maybe you'd refer to that person as "Panglossian", or "a Dr. Pangloss", after the highly optimistic character from Voltaire's Candide.
Or you might say she was "Polyannaish" or "a Polyanna", after the eponymous character from Eleanor H. Porter's famous novel Polyanna.
Welcome to Cloud Cuckoo Land!
From the ODO:
More example sentences: