What was your most expensive mistake?

Wrecking my first car....Don’t remember the exact cost since it was awhile ago but my insurance sky rocketed for awhile after it.

withdrawing from 2 subject with penalty it was 6600 aud ( I think it's around 5000 usd)

Buying junk stocks from rumours

It wasn't me but I remember when my brother was like 9 and spent $200USD worth of Robux (Roblox currency)

and he never used that account or XBOX again He got grounded for it...

Impulse purchased $800+ on eyeshadow in one go once. Severely regretted it a week later.

Forgot to cancel a hotel reservation. I don't remember if it was a hotel in Brittany or Normandy. Wait. No. I missed a flight. That was more expensive.

1,000 EUR on the driving school, even tho I realized that the teacher was horrible, I was too shy to ask for another teacher. Never be shy when using your money kids.

My mistake was 500 dollars.