John Aubrey* would have been a terrible man to do business with. By his own admission, he should have given his younger brother a large sum of money from the sale of land but instead ran off with it and went into hiding. And yet readers - well, this reader for sure, and I imagine many of his fans over the past centuries - not only forgive him but find ourselves nodding our heads in sympathy.
Aubrey knew he was a rubbish business man, he was aware of what he should be doing, but couldn't help himself from not doing what he should because there was always something far more interesting to research and study than knuckling down to boring business.
Let's face it, everybody does stupid stuff from time to time. Sometimes we know full well it's stupid but we still rush in headlong. Why? There's bound to be some psychological name for it, but I think it's simply an essential part of being human. If we only did sensible stuff, we'd never eat doughnuts.
So characters who never do stupid things, who are always perfect, who never ever get it wrong are characters we don't recognise as being human (even the ones that are aliens).
But in itself, doing stupid things is not enough for a main character - although it works for peripheral or secondary characters e.g. Father Dougal in Father Ted, Pike in Dad's Army.
Main characters need to have some self-awareness - like John Aubrey. They know they shouldn't stay for another drink because they have an important job interview tomorrow morning, but...they're human. They know they should rise above rudeness from their teenaged daughter, but find themselves snapping back.
Make your characters self aware; have them weigh up the options open to them. And then have them pick the least sensible one.
*The C17th antiquarian and writer, who I mentioned a couple of blog posts ago.