Because with the exception of academics, I'm quite functional on my own. I'm good at figuring out finances*, I want to move out/live on my own, I have reasonably good time management, and a very good work ethic (for work, not school).
My sister is the inverse, so I figure she's more likely to become the failure.
*Speaking of finances, what is a basic rule of personal finances? Underestimate income, overestimate expenditures. I follow that rule. My sister believes in the reverse, even when told her numbers are wrong, she ignores them.