Jim Collins picturized momentum, in his book Good to Great, as a flywheel.
Imagine the flywheel as being gigantic gear, meant to be moved in one direction. Push your shoulder into it, heaving with all your might, until it starts to roll. You keep pushing in the same direction, again and again, and the flywheel picks up more speed. Before too long, using the same amount of energy, you can keep it going in that same direction. Using that momentum is one of the keys to greatness.
Work at something long enough, for weeks, months, years, and decades, and you're bound to change the world. How much of the world is up to you and how much momentum you use. There are people I've met who try something new every other week. Sound familiar? Guess where they are a year from now. You guessed it: right in the same place where they started. If you stick to one thing long enough, you'll get good.
And then, over time, you'll get great.
Find your why, as Simon Sinek says, and put it into action. Today.