Getting stronger is a skill, and is no different from any other form of skill acquisition. In essence, progressive overload is the manipulation of some dimension of training in order to keep the exercise(s) challenging.

Strength training at its core is relatively simple.  There are five fundamental movement patterns that, when done two-to-three times a week, are more than enough for most people.  These movement patterns are: Push, Pull, Hinge, Squat (including lunges), and Carries.