I think it was Patrick Collison who also spoke about 'impostor syndrome' when joining YC. I imagine this is probably quite common. The whole question of what it means to succeed or fail is interesting; OP's perception of failure contradicts what I thought was the common view in SV - that to 'fail' (i.e. not get funding) is part of a greater process of learning and enhancement. I also can't understand how a 21-year-old Stanford graduate who already has experience in the market he's about to launch in could ever feel he "must have just been lucky".

>I also can't understand how a 21-year-old Stanford graduate who already has experience in the market he's about to launch in could ever feel he "must have just been lucky".

You don't seem to understand how competitive YC is. Guys like that are a dime a dozen when your acceptance rate is less than 3%[1].

[1]http://blog.ycombinator.com/yc-portfolio-stats

I completely understand how competitive YC is, I just find it hard to believe that anyone could doubt themself when they've attended one of the most prestigious universities in the world and also been accepted into the most selective startup accelerator. There's no 'luck' involved. This all takes immense talent.

>>"Success" is such a vague concept

Actually its not in terms of business.

Success = Profit + Long term sustainability in doing so.

Actually it's not that either.

Success in a business context means a positive rate of return on the resources invested. Or to refine one step further, a return that is positive and superior to the next best alternative for the deployment of said resources at a given level of risk.

So Profit.

ROI /= Profit.

See Amazon (or as noted below, Instagram).

However I also think that is a problem for many people who want to startup. They don't usually think about how they'll show a profit and manage to run their business within that profit. Investor money gets them started and an exit by selling an unprofitable yet growing business to a larger company is the goal.

Profitability and return on investment are related concepts but are not the same thing.

Instagram, among many others, most certainly generated ample return on its initial invested resources without ever generating profits.

Success can also be short term growth and being bought by a larger company, in this industry.

Success is the most loosely defined, illogical concept in the startup world. When your friends are raising big rounds, you think they are successful, even though most of them won't survive beyond the runway that round gives them (esp. at that stage).

Yet the media and the community celebrates founders for all sorts of things and call it "success" when it's not. So yes, it's incredibly vague, and the existence of an accounting formula means nothing in the founder psyche.