Every form of kindness you show is never in vain, it reproduces itself. Well, not necessarily before your eyes, but it always does. What is the glass of milk that you can share with somebody? Is is your time, a listening ear, a book, a piece of bread, a non-judgmental approach. Whatever it is, don't hold back what happens after the glass leaves your hand is none of your business, if it's not received well you gave with a good heart - so time will reveal that person's reward whether good or bad.