Haunted by the ghost of calculus past

I spent four years, 10 semester as a math tutor. Many of those years I spent helping out all the engineers with Differential Equations, Linear Algebra, or Multi-Variable Calculus. But, even during those years I inevitably had to go and help all of the young saps taking their first year of calculus. Helping them was never much of a problem, unless it was during the first week. That was the raspberry seed in my tooth for all 10 of those semesters. Inevitably every one of said saps would ask how to do each and every proof. These proofs were so simple, yet they would stump me every semester. I would spend hours trying to remember how I solved it just 4 months earlier.
One can imagine my discouragement and unmitigated rage when in my first class, after taking a 2 year hiatus, the entire assignment was made up of those very same problems! I guess it just goes to show if you don't learn how to do something right at first, you will be doomed to do it 11 more times.