How do you know what you know?

I don't mean facts like "blue+yellow=green", or "I wear a size 7 shoe", or even "I like raspberries better than strawberries." I'm talking about the things we tell ourselves we believe, things we think define who we are.

In other words, how do you know what you think about yourself is true?

For years I believed I hated writing - not that I wasn't good at it, as I had solid grades to prove I was at least above average on technical grounds, but that I disliked the act of writing. That I was a reader, not a writer. Then I started blogging and discovered that I quite enjoy writing. I'm still not sure my writing has any particular value, but I do, in fact, derive a fair amount of satisfaction from laying out my thoughts.

I thought I wasn't creative. Then I started doing crafts with my children and discovered I was fairly good at certain artistic endeavours.

I thought I was, at best, a mediocre cook, until my ex-husband stopped criticizing every move I made in the kitchen. Now I know I can reproduce pretty much any recipe in existence, and produce meals that impress my friends and family.

So why does all of this matter? Because I'm in the midst of wrestling with another opinion I've long held about myself, trying to determine whether there is actually any validity to it. I've long believed that I was not temperamentally suited to my current field of marketing, despite a bachelors degree and almost 15 years experience. I've thought long and hard about going back to school, starting over in another field. And I've been pushing at my current job to take on responsibilities outside the department, with the goal of gradually moving into another area. But I've got an interview tomorrow for a job that would be hard-core marketing, and a recruiter calling me about another marketing position. Both are pretty good opportunities - certainly good career moves on the marketing trajectory.

And I'm wondering if what I've told myself about not being cut out for success in marketing is really true, or if it's an excuse for not having done as well as I think I should have. Because if it's the latter, switching fields isn't going to make any difference - I'll undercut my successes there just as I do here.

How do you collect empirical evidence to evaluate your self-beliefs?