We humans have this strange habit of comparing ourselves to each other. But, we don't compare fairly. We are nearly always comparing ourselves upwards.
When you've got $1, you're looking up to the guy who has $100, thinking geez, I'm $99 behind.
When you've got $100, you're looking up to the girl who has $1000, thinking gosh, I'm always behind.
I get it. It's never enough. Us ambitious people always want to do greater things, which is not necessarily a bad thing.
It pays to look back from time to time, though. Take a look at where you've come from, and all the things you've done. Remember the time that $100 felt huge. Be proud of yourself.
I'm not talking about money, by the way. The same is true for your skills, your job, your role, your level. Anything.