This depends on why you’re donating. If you’re trying to get the mental state of feeling ‘I did some good’ or you’re trying to impress your friends/family (certainly legitimate goals), then this logic might work. If you’re trying to help people as much as possible then this logic does not work because the amount you expect to have helped people rises linearly with the probability that the charity helps.
One common strategy is to spend a smallish amount of money giving to various causes that make us feel good and/or impress others and a larger amount of money on a single charity optimized for helping people as much as possible.
This depends on why you’re donating. If you’re trying to get the mental state of feeling ‘I did some good’ or you’re trying to impress your friends/family (certainly legitimate goals), then this logic might work. If you’re trying to help people as much as possible then this logic does not work because the amount you expect to have helped people rises linearly with the probability that the charity helps.
One common strategy is to spend a smallish amount of money giving to various causes that make us feel good and/or impress others and a larger amount of money on a single charity optimized for helping people as much as possible.