If you do, your brake fluid will expand under heavy braking, and with no space in the reservoir it will close up your brake pads and lock your brake. While you are trail braking... at speed.
And you won't remember it. Because you'll land on your head.
Same orthopedist, same finger, different situation - no pin or surgery required this time - it's been in a splint for a week and a half - it came out today, and now it's taped to its neighbor for a few weeks.