‘To write something off’ comes from finance but its figurative meaning is to declare that something or someone has failed.
I was hoping that the new employee was going to work out but it’s time to write him off. (There’s no chance he’ll be able to succeed)
He seems too short to play basketball, but don’t write him off. He’s an incredibly good shooter.
A couple of months after COVID hit, I wrote off 2020 as far as traveling was concerned.