Generous people are investors: they spend resources on things that don't yet pay off for them directly, but that they see as valuable more broadly.
Stingy people only do things that directly benefit them in the here and now.
Long-term, generous thinking makes you better off.
Example: a neighbor you don't know (or even like) needs one-time financial help.
If you can afford to, help them out.
Having a thriving neighbor means less poverty, crime, upheaval, etc. in your neighborhood. And they may (not guaranteed) help you out when you're in trouble.