At the risk of sounding harsh, this is an incredibly silly way of looking at things. Of course you can be successful. And I'm not speaking from a toxic social-Darwinist mindset; there really are people out there for whom the cards of life are stacked against them and no amount of bootstrap-pulling is likely to change that. But an engineer who graduated from an accredited college (assuming there aren't additional circumstances) is not one of those people.
I would guess that your definition of "successful" is set unrealistically high, and/or you've burned-out when it comes to moving above what you consider to be "mediocre". The former can also lead to the latter.
I recommend re-evaluating what will actually make you happy. Take a critical eye to the expectations you place on yourself and make sure you're only hanging on to the ones that will make you yourself happy, not the ones that society, or your parents, or anyone else has given you. Alternately, for some people, having expectations at all is problematic. Some people (like me) thrive in the absence of pressure and get paralyzed by it when it is present. It could be that you just need to give yourself a break and ask yourself what you want from life, instead of what you think you're supposed to want. Everyone's different.
Best of luck working through all this.