I have to agree with the perhaps inappropriately named logicallee. And I'd go further - it's not just a matter of age, nor (as others in this thread have said)

I have to agree with the perhaps inappropriately named logicallee. And I'd go further - it's not just a matter of age, nor (as others in this thread have said) of inability or stupidity, if someone works for a salary under market value. I am far from the best at my job in the world, but I'm ok, and for the longest time as a freelancer I charged way under the market (in fact I suspect I still do, though not so egregiously). This was - I think - not because I "overestimated my ability" or anything like that. I was simply not a business-minded person. I was afraid to ask for more. I earned enough to live from, and the rest seemed somehow distasteful to me. I'm not saying this is the ideal, just a fact. And if I have these characteristics, perhaps others do too.