Be Kind, but don't give anyone the opportunity to think you are stupid, you shouldn't be the one doing the kindness all the time while the others sit and enjoy your kindness.
It is okay to open the door for other people sometimes, and it is also okay to wait for others to open the door for you.
Don't waste kindness, keep it for people who really need it. When you abuse/overuse your kindness, you will feel bad when it's not be reciprocated, you are just human.
This is very important especially in this dispensation, be kind but don't allow anyone use you or make you feel used.