Human nature is hard to change. Also, what we regard as bad habits
have payoffs, either directly rational or unconsciously emotional--or
maybe both--that we denigrate too much when we try to change our bad
habits. Don't knock those payoffs! You choose to eat too much of
something because it tastes really good and KEEPS tasting really good
no matter how much of it you eat. You choose not to exercise because
the TV show is really good or the video game is extremely compelling
and rewarding and fun.
If you want to change a habit, take it slow, in definable steps, with
regular checks on your progress. And don't beat yourself up! Unless
beating yourself up works (because every piece of bad advice is really
good advice every once in a while).
Furthermore, I don't think things worth doing are necessarily hard to
do. But they may be hard for YOU to do. And then you may want to
consider whether it's necessary to do them at all.