Every successful Youtube niche has an emotional spectrum:

#1 Finance: Curiosity-Urgency

Curiosity: Is this actually possible? Can I do this? Did he actually do this? What did he do?

Urgency: Use of a time frame in the title (90 days) creates pressure to start immediately

#2 Gaming: Excitement-FOMO

Excitement: Destruction is involved

FOMO: Need to know the answer/see the explosion

#3 Self-improvement: Hope-Transformation

Hope/Transformation: For energy and change of lifestyle

#4 Drama/Commentary: Shock-Validation

Shock: Popular streamer has dark secrets

Validation: Validates a viewer's suspicion

Your thumbnail should hit the exact emotion your viewer expects to feel.

Wrong emotion = wrong audience = bad retention