You probably won’t remember this, but the “forgetting curve” theory explains why learning is hard

Learning has an evolutionary purpose: Among species, individuals that adapt to their environments will succeed. That’s why your brain more easily retains important or surprising information: It takes very little effort to remember that the neighbor’s dog likes to bite. Remembering the dog’s name is harder. One ensures safety, the other is just a random fact.
But today, the kinds of things humans want to learn are rarely focused on survival; we also use our adaptive, evolutionary memory to remember new languages, 11-step face-washing routines, obscure vocabulary words, and facts about Star Wars. The trick to doing so, once you’ve decided to acquire a new skill or build up your knowledge in a particular area, lies in convincing your brain that the information matters. In other words, you have to overcome the “forgetting curve.”
Hermann Ebbinghaus’ memory experiments

The forgetting curve is a mathematical formula that describes the rate at which something is forgotten after it is initially learned. The idea is over 100 years old. It originates in the late 19th century, with German psychologist Hermann Ebbinghaus, who was among the first scientists to perform experiments to understand how memory works.