The money I contribute always comes back to me multiplied.

Somebody covered your rent once, or filled a fridge in a month nobody was talking about, and never mentioned it again.

What comes back rarely comes back from the same direction. The person you helped in 2014 is not the person who helps you in 2027. It travels sideways through a network whose shape nobody can see, and the multiplying happens well out of view.

That makes it a hopeless investment and an excellent habit.

Give with the arithmetic switched off. The ledger it belongs to is not one you get to audit.