Having long passed the age of 16 and well into my early 20's I've finally decided to start learning algebra > geometry > trig and eventually calculus. I'm 2 weeks into teaching myself algebra and I have a question for the professors. When teaching students, what is the most common problems that students have when you're explaining something new? Also to students, when learning something new, what is your biggest problem (if any)? For me it's remembering the rules and equivalences. Even though I have not learnt any calculus yet and I can't even read calclus problems. I've just started to learn about sin, tan and cos and remembering SOHCOHTOA is pretty simple but it gets pretty complicated by the looks of things once I get passed the first page of the book. Do you lecturers literally never forget a formula? Never forget a rule or an equivalence? How do you remember it all !