One man's loss is another man's gain proverb
The phrases one man's and another man's can be replaced by names or pronouns.
When someone loses or gets rid of something, someone else has chance to take it.
Someone threw away this cute teddy bear. Think that one man's loss is another man's gain, I took it home for my daughter.
Our company recruited our rival's employees when their business closed down; their loss was our gain.
When he was about to throw away the hamburger, a homeless approached and pled with him for it; one man's loss is another man's gain.
The origin of this proverb is not clear.
People tend to remember the bad things others do and while they easily forget or get rid of others' good things.