I have never used a quadratic formula, either, but I had to set up and solve 40 equations with 90 unknowns.
I once hired someone just because she demonstrated how she could learn on her own. Her prior company was stupid to let her go, she was so good!
I also joined Toastmasters. My worst speech ever was one that I had to read word-for-word to get certified. I had already given speeches at national conventions, but I wanted to learn new techniques.
You never know in advance when you will need to know something or what it is.
I have used information that I learned 20 years ago.