Ask HN: Have you ever taken a chance on someone and it didn't work out?

I've heard of many success stories of someone taking a chance on someone else, either giving them money, a place to stay for a reasonable price, or even sponsoring their education, and that person turning their life around. But I've encountered the opposite: everyone I've taken a chance on has disappointed me, taking advantage of the opportunity I provided for them, or it just ended up not working out the way I thought it would.

Recently, a childhood friend of mine was down in the dust, and had his criminal record expunged for marijuana possession (jailed for being near a school) since it's technically not a crime anymore. It was just a case of being at the wrong place at the wrong time. People aren't the same as they age, though there is a general part of their personality that usually always stays the same, but when I was younger, he encouraged me to not allow myself to be bullied, so he's a guy I looked up to. My mother also babysat him and his sister. So he wasn't a complete stranger to me.

I offered him a place to stay on the condition that he get a job and pay his rent. I'm a contract man so I wrote up the contract and we both signed it. He's been a good roommate as far as one could ask for.. quiet, kept to himself, cleaned up after himself, and was paying his rent up until a month ago. He'd been living with me for just 4 months. I don't know what happened, but it was like he just decided one day he wasn't going to work or pay rent anymore, and I approached him with an eviction notice: pay up or get out. I thought I was helping someone out but ended up just getting screwed by thinking he wanted to better his life.

Care to share your stories?