A small act is like a seed which can grow to become a big tree where the birds and passersby can have shade on a sunny day and whose fruits can also become trees. The multiplier effect of this is a forest (like the Amazon) being birthed.
Remember that song by Jack Greene?
"You got to try a little kindness
Show a little kindness,
Shine your light for everyone to see
And if you'll try a little kindness, then you'll overlook the blindness
of the narrow-minded people on the narrow-minded street"