Ask HN: How important is it to feel challenged by a potential job?

So I just interviewed with a software company. It went really well and they made me an offer that meets my salary expectation. The team also seems friendly, and I feel like I'd enjoy working with them. But there's something missing—namely, it feels too easy.

Is it reasonable to think a company might be too good a fit for you? That its work might not present enough of a challenge?

If so, how do you distinguish between a reasonable sense that a job won't be challenging enough and an arrogant one?

Also, one implication of it not feeling challenging enough is that I suspect I could get a higher salary offer somewhere else if I did a proper job search (this was just a one-off application).