When a mathematician makes a mistake...

How embarrassing is it if a mathematician submits a paper to a preprint archive and then it is found (either by the author or someone else) that there is a mistake?

(I mean one that is difficult to see even by experts, not something completely ridiculous).

Do people think they were lazy or stupid not to have realised?
That they can't be good mathematicians and are letting everyone down? Or is it quickly forgotten as something fairly respectable and routine?
.