Everyone loses motivation, you're right about that. But you have to think about what's important to you in life in order to succeed. Nobody got where they are by staying in one place.
When i work, study, or otherwise do something meaningful in my personal life, i try to put my heart and soul into it, because at oftentimes a job half done is worse than nothing done at all.
Don't get me wrong, i hate effort as much as the next guy, but i know that i could never forgive myself for failure if i haven't given it all i got. Losing an opportunity to inaction is the worst crime the oblivious can commit.