So many things.
We had a small inheritance and got sweet talked by a salesman to sink it, and money borrowed off my parents, to buy a student pod in a big city.
Turns out the market was saturated, the property was miles away from the uni, and the developer was a known con man who had done jail time.
We had a year's guaranteed income, which, it turned out, was paid out of the capital we and others invested. After that year we never saw a penny and it was never even close to full. Then we had to put more money in as there was damp, there was a fire, and all the while massive council tax bills because no students were actually in residence. Now it limps along earning about £30 per month and can't really be sold. I still owe my mum £30k and my husband sort of feels it was my idea. I am utterly depressed and as have mentioned elsewhere have pnd to boot.
I found a pound on the floor yesterday however so felt I was winning for once 
We parked our car outside our house once (in a city, in a bay) and the next morning the over eager council had taken it and crushed it. What can you do? The car was worth next to nothing, but of course it cost thousands to replace.
I quit my job losing a year's earnings and adding 16 thousand pounds to my student loan in order to train to become a teacher. I am above average in my specialised subject but they don't tend to test it at interview so I spent years competing against less good teachers for jobs. The subject has a very high unemployment rate. Once I did supply and we were 8 ladies in the school that day (the entire English dept was on a jolly). We laughed when we found out that we were all teachers of my subject (it's not English). Also it turns out I don't really like teaching due to the hours and stress. Royal waste of money and now I feel pretty much good for nothing, work wise. The kick in the teeth is that they now offer 25k golden hello for my subject. Rats!
So relieved to be on maternity and I would have paid £16k plus £25k just to have my beautiful baby though!
Peace and love to all mums, life has ups and downs but tell yourself so long as we have each other it'll be alright.