When doing any “thing” (process/procedure/etc.) it is important to do things in the proper order. Otherwise, whatever one is attempting may simply not work… (at least not in the way that he or she is intending.)
Even THIS house was built “From The Ground, Up”.
It also implies that one should start with the basic necessities and/or “first steps” before doing other things which (though they may be more interesting) can only be beneficial after the foundational elements are firmly in place. .Because it is basically impossible (at least in this version of reality) to build a house from the roof, down.
“If you want to become a superhero, you gotta build from the ground, up. In other words… First you have to learn acrobatics and martial arts. Then you need to find a secret underground lair to hide all your awesome gear, and THEN you can worry about the kick-ass lycra suit with matching cape and mask… get it?”