I love words...
I was just doing a bit of writing and found myself using the phrase "I am not cut out for that" as part of an example.
It made me think - it's a common piece of language and it implies that we are 'stamped out' of some ethereal dough like a gingerbread man with a cookie cutter.
Another manifestation of this idea is the old "I'm not the sort of person who could do that."
They're sneaky self-limiting statements that are bandied around a little too much I think; although of course there are situations where the "I'm not the sort of person who" would apply:
I am not the sort of person who could be a world-class jockey: my dislike of horses I could get over, but being 6'6" tall is a major hindrance
Just a little bit of musing...
Roger