This is a common behaviour among the people in general. If you manage to do 19 things right out of 20. It is only the one you do bad people will always remember. They forgot that not everyone is perfect. most times I don't care if I don't get paid for whatever I did because I did it for myself.Come to think of it, most employers do not hold back when criticising employees for their mistakes. So, they should also try to give the same energy when praising them at least.