tell me the secret!

so i'm wondering... what's the secret?
have you ever gone thru phases of excitement over something only to find that over time it wears off? why is that? is it lack of motivation, inspiration, determination, a combination of all those and more?? i definitely have and i'm wondering why? 
here's an example- about a year ago i stumbled across a book written by a coupon crazy mom (and I do mean stumbled because in no way would that have been a book i would have sought out). so i read it, i checked out her website, and the craze began. i bought a little plastic file to help me sort and organize my growing pile of coupons and i began what turned out to be a crazy adventure in saving money and grocery store hopping. BUUUT over time i lost that crazed interest i had and fell back into the ol' routine of buying what you need when you need it, for the most part. Why is that?? When and what is it that may have caused that excitement to drop?
I could go on and on with numerous examples of other areas but I will spare you details and just ask if you know what i mean? and if YOU HAVE THE SECRET of how NOT to lose that Please fill me in on what it is! I mean even God knew people would be this way because you can find in His word where He tells us to "Stir yourself up" not to rely on others for encouragement all the time. So if you have some "stirring" ideas please make me and others aware of what they may be! 
I must add though... the BIG things in life I usually don't have problems with, but there are plenty of other small, could be beneficial, things that I would appreciate help in knowing what others do to keep it up?!