Success, money or not
I would be lying if I said that the notion of successful publication didn't come with some sense of validation for the creative overachiever. Is it the only marker of talent? No, of course not. Plenty of incredible works are passed over for a myriad of reasons and as long as humans find solace in ease and familiarity, mediocrity will also be elevated. (Not to say that an incredible piece of writing can't be easy or familiar to its reader).
To me, traditional publishing is external validation combined with the promise of publicity or profit, however meager it may be. It is someone else in your "world" seeing your work, saying "No, you're not delusional- this does indeed deserve to be shared with the world" and being moved enough to offer compensation in one form or another. You've cut through the politics, through the arrogance of artistic sentiments and creative cliques. You've learned to speak from your own beating heart to the beating heart of another in a way that is not just personal, but professional in the most black and white of ways.
Self-publishing is a different mountain to climb. It is brave, it is bold, it is looking in the face of established systems and choosing to go your own way. But that independence comes at the cost of money and time. You have to learn more, do more. Success rises and falls upon your shoulders. The greater the risk, the sweeter the reward. If traditional publishing is like a slot machine, self-publishing is when you brazenly try to bet against the house.
Both require sacrifice. Both are lofty pipe dreams, depending on the end goal. Neither are necessarily markers of talent or personal success, but the notion is still quite alluring.