You've seen what it looks like when you take a ball and roll it down a hill. The longer distance it travels the more speed it picks up and consequently the larger impact it makes on the object(s) it connects with.
This is a universal principle. The work that you do needs for you to gain traction and start picking up speed. But you can't do that until you've first traveled a fair amount of distance. You always run faster after you first covered some ground.
The hard part is getting started. Getting started means that you have nothing "real" to feed off of yet. It's all potential. Like potential energy - it's not kinetic. So you can only think about what things could be like and start the race from there. But over time and distance you begin to learn from mistakes, understand how to be more efficient, and recognize the importance of scaling. Suddenly, your work begins to take on a life of it's own and before long you got some momentum.
Seeing momentum at work is like watching a magic trick - there is no simple explanation for how it all works--but it works. However momentum is difficult to build. It's not just the effort one needs to put in that matters - it's also the length of time they have to spend doing it that makes the difference.