Display flashes and nothing else happens

I flashed my first firmware and now the display just keeps flashing?

Answering my own question (from the library README):

If the display flashes every second or so (and not much else happens) then
you may be in a “boot loop”: the device is starting up, crashing, then
rebooting… The solution is to fix whatever pathology is in the last
firmware you burned and reflash. Check serial to figure out what is
happening on the board.