Happiness that you strive and gotten, you will remember and
treasure, thus it will seemed sweeter because you work for it.
Remember the time when you did your first job and gotten your first
pay? The feeling is good and especially if you spend your pay on
something (Like enjoying the result of your hard work) 
Happiness that is given naturally by fate, for example a good
family, you would have another sort of feeling - feeling blessed
and thankful. But such situation are normally situation where you
cant do anything about - you can't choose what family you which to
be born in right? So when you are in sensible age - many things you
have to fight for it - if not somebody is gonna come in and take
what originally seemed to be yours. 
Cheers
