Spare change seems pointless until you count the jar. Small kindness works like that.

Individually tiny things look like they do not count, which is a mistake about arithmetic. One coin is pointless and nine months of coins pays for something, and the same holds for held doors, answered messages and remembering what somebody told you last week. None of them amount to much on the day. Added up, they are most of what people mean when they say somebody is good to them.

Do the small thing you normally skip for being too minor to bother with, a few times this week, without counting. Nobody will mention it, and it will still be in the jar.