I know what it takes. I haven't done it, but a couple of my friends have, and they've described the herculean effort required. The things people usually expend their effort on

* Maintaining relationships with friends, family, and loved ones

* Excelling at their job

* Reducing bad habits(like drinking, tv watching, smoking, etc)

* Pursuing hobbies

* Raising children

And all of them have had to make significant sacrifices across the board to maintain their weight.