Pretty much everything we choose to do is for the purpose of making ourselves happy (and whether that comes as a result of making others happy).
But in those times where you are denied something, someone ignores you, things don’t go your way or your lofty plans fall face first in the mud, it may be just as important to learn how to let yourself feel sad.
Acknowledging, embracing and letting those melancholy feelings sweep through you may be necessary for you to truly connect to future great joys that come into your life. And they likely will come.