[Bahamut]

I had an interesting transition from high school to college as well - I aced math classes beforehand, doing well in courses such as college Calculus III, Linear Alegbra, and Differential Equations, but ended up failing an intro proof class my first semester of college.

After failing that class, I still took enough from it to pass subsequent proof-based math classes with good grades. Ultimately I left a top PhD program in math after 4 years and did well for myself since that failure, but it's interesting to note that transition from easy & menial calculations to full-on hard logic that challenges you at the highest level mentally. Our education system does a poor job of preparing us for it.

Edit: For further context, I was a top math & science student in NY, having placed top 50 in competitions nationwide and similarly competitive state and region-wide