Hey peeps who are 40+ — what advice would you give the younger generation?

I was recently talking to my grandpa about money. He told me to always save for a “dry spell” before spending, and then showed me the small FDs he and my grandma had been making since their college/early working days.
Seeing those little deposits still sitting there after all these decades was oddly nostalgic. It also got me thinking about how different personal finance is today — SIPs, stocks, credit cards, BNPL, UPI, etc.
So for those of you who are 40+: what’s one financial lesson you wish you had learned when you were younger?