Use 'count out' when someone might still surprise you. It suggests they're not finished yet! Many thought she was done, but don't count her out—she's full of surprises.
Pro Tip 2/3
Relevance Matters
'Count out' often implies a change that's made someone or something no longer relevant. Technology changes fast; count out yesterday's gadgets.
Pro Tip 3/3
Underdog Support
Use 'count out' to show support for underdogs, indicating belief in their potential. He's a new writer but has great talent—don't count him out.