underestimate

1: Always and inevitably, everyone underestimates the number of stupid individuals in circulation.

But he severely underestimated the project.

4: Non-stupid people always underestimate the damaging power of stupid people and keep forgetting that to deal with stupid people always turns out to be a costly mistake.

If we do, we not only overestimate them, we underestimate ourselves.

And we kinda had an oh shit moment right after that Elwynn Forest play test, where we realized, like, we had vastly underestimated the number of quests we were gonna need.