You want happiness for yourself. It is much more generous to give it. It is a good practice to give happiness.
Giving happiness often requires some level of self-sacrifice. Self-sacrifice will give your life meaning in areas where it previously had none. It will also make you a more tolerable person.
The more tolerable you become, the more others will feel compelled to lend happiness back to you. So by giving away your trickle of happiness, you will have a wave returned to you.
That also means you should then give more happiness as you have now received an overabundance. We seem to handle scarcity better than abundance anyway. The balance is just right.