Successful seems to imply there are no downs to the ups. Successful seems to imply that you actually figure shit out and it stays figured out.
Anyone who says they've figured it out is lying or has completely given up. Neither seems "successful".
I care more about longevity than success. Longevity implies that at least some things are working, at least some of the time, with enough momentum for the good bits to outlast the bad bits. Longevity means not that what I've figured out will stay figured out but that I won't ever stop trying to figure shit out.
"The purpose of life is to be defeated by greater and greater things."
Rainer Maria Rilke
The reason I choose the career I have isn't because it's easy or simple. It'd be easier to work for someone else. It'd be simpler to do only one thing instead of many.
I do what I do because I crave the fight of challenging the unknown. Sometimes it kicks my ass. Sometimes I land a couple of good blows. Yet neither of us ever steps out of the ring.
A long-lasting career, at its absolute essence, comes down to three things:
1. What you can do
Never stop refining the skills you have and learning new ones. Ever.
2. Who you know
3. What sets you apart
Regardless of your skillset or who you know, 99% of what you do is the same as your competition. Web designers are all skilled at web design. Writers all know how to write. The remaining 1% is unique to you. That's what sets you apart.
The last 1% is how you stand out, differentiate, build an audience, establish a massive client roster, and become known. This is the most difficult to figure out and most scary to work on. Because it's you--the real, honest, vulnerable you.
The more you work at your long career, the more you'll realize that is why your career exists--people hire you because you're you, and not just because of what you know how to do.
Longevity comes from working at those three things.
So never stop learning, exploring or building upon them.