Bought a mobile home as a starter home. No one ever explained to me as a young adult the importance of investment and future planning. Mobile homes of course do not hold nor increase in value so you never build equity. It's akin to renting except you have to cover all your own repair costs too. Terrible financial decision.

When I turned 21, I gained full control over my inheritance account. It was how it was written in my grandparents will. At that time, it was only worth $15k. It was the only time my financial advisor ever met with me. I said I wanted to invest all of it in AAPL. I still remember the face he made in disgust. "Why would you want to invest in Apple?" I explained that I had just done a college paper on Steve Jobs and I truly believed that now that he was back in charge of the company, he'd turn the stock around. He convinced me to stay the course and keep the same investments.

Hate to admit it, but I got nailed by a crypto scam. So dumb.

Kept my money in a bank ($ 150,000) because they were offering high interest rates in a country with questionable economic conditions. The entire system crashed and I can't access my money.

Sold my signed Banksy prints for a couple of grand to fund a new kitchen. Saw the same prints a couple of years later selling for £80,000.

I discover bitcoin very early: I bought 100 of them at 63 cents a piece. Sold the whole bunch for 300 dollars.

Student loans.

5 years ago I bought plane tickets for my ex to come and see me, he cancelled on me 3 days before saying his grandma was on her deathbed. She wasn't. I was 16 and I wasted 3 years worth of savings.

Credit card debt. Finally paid everything off when we sold/bought our next house and made the promise to never carry any credit card debt. And we haven't.

Becoming a doctor. At the end of the day, it’s just a job. It wasn’t worth flushing my 20’s down the drain and accumulating a mountain of debt for this. I’m (finally) in a good spot now, but I don’t think the sacrifices I made to get here were worth it.

At the height of the pandemic, I had a pretty severe "hidden" mental breakdown due to the trauma of isolation/quarantine and general terror over the whole thing. Combined with my own long-standing battle with Bipolar Disorder, I wound up withdrawing €4,000 from my savings account and going on a massively impulsive shopping spree.

Agreed to take over my ex gfs bills so that she could pay off her debts. 5 years and over $100,000 of my money later she was in more debt than when we started and cheating on me. Don't ever do this, just make her be an adult.

Going to college right out of high school. College is great if you know why you're there, but not for someone who isn't yet sure. I can't speak for everyone but when I was fixing to graduate high school back in 2000-2001, everyone thought college was the next step because literally no one ever told us anything different.

Didn't contribute to my 401k for like 15 years.

Nearing the end of the dotcom boom (it hadn't busted yet) I had many stock options to exercise. I was about to do it, when I heard that my Dad was entering the hospital for a cancer operation. I put the stock options exercise on hold for a week and went to be with my Dad. While my Dad was in the hospital, my company released an earnings warning and our stock price got annihilated. When I did eventually exercise my options, I was down about $1,000,000 from where I was before my Dad entered the hospital.

I went to America for 10 days to visit a buddy of mine. Cost me a fortune and I arrived to find he had been absorbed into his new girlfriend and was not the guy who left. Anytime he was away from her he was miserable and didn't want to do anything.

Not mine, but my dad's. He bought like $500 worth of collectable Star Trek dinner plates in the 80's thinking they'd be worth a ton of money in a few years. They're not.

I invested $890 into a stock and it later became a little over 1.5 million dollars. I did not take the money out because I thought it would go up. I quit my job because I thought I was going to be rich. My stock crashed to worthless, I’m struggling to get by. I could’ve had a house, started a business. Now I have nothing.

Sold my MTG collection in 1998. Almost full power 9, 40 revised duals, all the playable cards from beta, legends etc. Sold them for $1000 and bought booze and meth. Would be able to pay for a house with those cards now.

I was not good at checking my company email inbox, nothing important came through there anyways. And that is how I missed the deadline for my company’s IPO. They offered us stock at $10 and it opened at $40. Now I read my emails.

Bought a condo in July of 2007. The timing literally could not have been worse. Could have bought it for virtually half the price if I waited a year. Sold it just last year for less than I bought it.

Spending all my student loan refund checks instead of saving those to PAY OFF MY STUDENT LOANS.

Lost the wedding ring. Seriously I lost it.

I inherited money from my mother after she died. Instead of retiring my mortgage I used it to renovate my house to add two bedrooms and a bathroom. My thinking then was that it would be nice for each of my kids to have their own bedroom.

Bought a stock way back in 2014, it jumped by like 60% in two days. I went to sell, but got a phone call and got distracted. Remembered it the next day, and it was only up 20% from when I got it. I thought to myself "lets just wait and see" hoping it would jump back up. It never did. I eventually sold it at a 60% loss a year later. Was only a 2k investment, so not a huge loss, but would have netted me a quick 1k in two days if I had just ignored my mothers phone call.

Took a job way up North in Canada. Quit my old job, got rid of tons of stuff, had my dad help sell my house, etc. This was in 2019/early 2020 just before COVID hit big. I ended up hating the job up North; it was terrible. Went back home, somehow managed to get my old job back, but my house is gone and I can’t afford a new one in the current market. Stupid, idiotic decision on my part.

Gambling.