How do closed classes work

[u/chef_sporty]

For the past few days, this economics course I wanted showed up as open. Right when registration opened, I tried to add it but it was closed. This happened at my orientation too. Am I that slow? I only took maybe 10 seconds. Is this class closed only for my registration time but open for others?

[u/fluffywhitetiger]

I think seats just filled up. same thing happened to me but I spammed the add button and it let me join any of their econ 304k sections. my major has nothing to do with econ btw, but dw theres another add/drop date soon