Most of us have had the experience of having a goal, and knowing what we're supposed to do to achieve that goal... and yet not doing it! "I should be out at the gym... which is only 150 metres (yard) away... right now. I'll do it right after I clean this popcorn popper and check my spam e-mail folder to be sure I haven't missed any big financial wins from Africa!"
A big reason for this is because we may be pursuing something that isn't REALLY important to us. When we are faced with a change of habits, "...we need to activate a part of the brain called the ventromedial prefontal cortex, which is simply the part of the brain that processes risk and fear. It also plays a role in decision-making and habits."
There's a quick exercise you can follow to determine if you're really trying to change a habit that is inline with your core values... because those are the only habit changes that have a decent chance of sticking!
http://www.abc.net.au/news/2016-01-12/finding-your-why/7083666