Can’t comprehend the time in the market advice

Someone ELI5 how is it better to invest a lump sum at the all-time high right now, than wait a few/several years for a dip/crash?
The Ukrainian War doesn't look like it's going to end soon, the Middle Eastern crisis/war, possible conflict over Taiwan, the AI hype is worn out, etc.
What gives you a reason to be bullish short/mid-term?

EDIT: Thank you, everyone, almost every comment was very valuable!