In the age of clipper ships and bodices and Jules Verne, stepping on the moon was pure fantasy. A century later, it was in the newspapers. How does the transition from magic to manifest take place? Sometimes, if you do the math, you can do anything.
This will infuriate my high school English teacher (sorry, Mr. Skilleter), but some challenges in life require a bit or reckoning. Yes, you need imagination, willing minds, and a vivid vision of your future. But even pursuits less celestial than space travel take the crunching of numbers.
Want to learn to paint/sew/write? It will take time. How much time? An arbitrary stab says 500 hours. Where will you find those hours? Perhaps you have two whole hours a day (one before and one after work). That's 10 hours a week. Do the math and you have your still life/romper/screenplay in under a year.
"Do the math" simply means "figure it out."
Figure comes from old Latin, figura: "Lines forming a shape." We use figure to mean a numeral, or a picture, or a body. As a verb it is more potent. To figure is to believe, to calculate, and ultimately to appear. It is imagination, a willing mind, and a vision made manifest.
Every audacious mountain is a sum of modest boulders and timorous stones. Doing the math reveals the routines you need to climb the unclimbable and Routine is doing what you want. Do the math and even the impossible becomes possible.