Duty friend or foe??

Is strange how when I start doing something because I like it is easy for me to do it, but as soon as it turns to be an obligation I loose interest, obviously I push myself a little harder to finish whatever I started now that is a duty to do excluding that now my heart is not into it so if I could have done it with all my might then the work could have been a hundred times better than the final outcome, except that if it wasn't an obligation maybe I wouldn't finish it at all XP.