You might think
I have always done xxx
but maybe you have always been in an environment that makes it easier for you to do xxx than not to.
So it might be very very difficult (and feel impossible) for you to change that behaviour in your current environment.
But if you changed your environment, you might then find it easier to make the change to your behaviour.
Example 1:
behaviour is feeling negative about yourself
environment is spending a lot of time with "friends" who you've known since you were at school who have always seen you as "the fat one" or "the less-clever one" who they keep around to make themselves feel better and like to put down
Example 2:
behaviour is not bothered to go to the gym
environment is live far from work and school, have to travel specifically to gym rather than going there on the way home
I didn't say it was easy to make the change to the environment, just that the change to the behaviour would move from "impossible" to "possible", if the change in the environment could be made.
This only counts if it's YOU, of course.
If the person who you think will never change is another person, they probably won't, because they probably don't want to.