If it is something that you want, whether it be in health, life or fitness you need to put 100% effort in to reach those goals/dreams, you aren't going to reach any of these things if you are just doing it half ass-ed and putting 50% in. Giving 100% is important because it increases the chances of being successful in what you do.
"What you get out of each day depends on what you put in, and that is entirely up to you"
Some reasons you may not be giving it 100%
Don't be one of those people who just plod through life, do something worth while. If there is one thing I have learnt in my time at a desk job, its that there are opportunities way more fulfilling that do not involve a desk, something you will actually get joy from, something where you are not just a number, somewhere you will be valued.
Life is too short to be anything but happy, so give it 100.