I think one of the hardest things in life is just consistency. If you can choose something, and stick to it until the very end.
For example, there are Japanese painters who specialize in just cats, just bamboo forests, just fish. Their level of skill becomes almost godly. The reason they become so skilled, is because they were able to commit!
And so, it seems to me, that lack of success is really lack of commitment: to pick one thing and to practice it every day, day in and day out, focusing on that one thing. Can you really fail to achieve amazing heights with that kind of focus?
And again, that ability to commit is so rare, that we view people that have it as superhuman. But commitment is a choice we make daily, just as we choose to love someone every day.