Mugger: If you have the guts to pull a gun on me, I'll probably get nervous and misfire in my attempt to rob you.
Otherwise, if you give me $15 of the $25 in your wallet today, I promise not to try to shoot you and take the full $25. But in the likely event that I run into you again in the near future, I'll probably still try to shoot you and take everything you have that day. Except in some extraordinary circumstance, like you really, really need the money, or something like that.
Victim: What a great day!