Who Are Adventurers?

My friends and I have talked a bit about this at length. 

Many fantasy roleplaying games assume "adventurer" as a profession (even if just implied) and, to one degree or another, "adventurers" as an important cog in the machine that drives the setting's economy. What they don't often do is ruminate on who adventurers are and why they do what they do.   

I theorize that adventurers are either desperate folks, fearless folks, or foolish folks. I mean, if you look at adventuring as a profession in the context of most common fantasy settings, what reasonable person would pursue that life?  

The risk of being a professional adventurer is high and, while rewards can be earned, there are absolutely safer, more lucrative, professions in most such settings. A jeweler, money lender, or even just a shrewd merchant, for example, probably earns magnitudes more money than your typical tomb-looting vagabond - and without risking their lives on a daily basis. 

So.

Desperate folks. Everybody needs to eat. Even in fantasy land, this is a given. If you don't have any marketable skills and haven't inherited a business or monies, you have to make money somehow. Anybody can loot a grave or raid a tomb. People have historically engaged in such activity in our own world for similar reasons. This is understandable. 

Fearless folks. Daredevils do exist. People who indulge risky activity purely for the associated thrill. This is slightly less understandable because, in my opinion, it's not entirely rational. Ostensibly, the greater the risk, the greater the thrill, which is why these folks would rather wade knee deep into a horde of hungry undead than, say, climb a mountain. Such people are, to my mind, dangerous. 

Foolish folks. Everybody knows at least one fool. These are the folks who just don't do the math and have visions of fame of untold fortune in their heads. And maybe they'll prove me wrong, but in my experience, such folks either end up dead or not substantially better off financially at the end of their career as a professional adventurer than they were at the beginning. Fame and fortune are, on most days, fleeting at best. 

So, who is your adventurer? A desperate man or woman who has mouths to feed or debts to pay? A thrill-seeking daredevil who seeks out adventure for its own sake? Or a foolish person seeking to enrich themselves in what is quite possibly the riskiest way possible? And what does examining adventurers through this lens imply for your setting? 

Some food for thought.