Yeah, changing thought is a skill, as any physical skill, everyone has a different pre-disposition and ability to learn.
If you don't know how to strengthen your abs, exercise, and eat right, you will have a flabby belly all of your life.
Don't downplay habits. Habits are the brain's form of keeping in practice. Habits are a bigger deal than anything else you can think of. Bigger than a fatal car crash, bigger than suicide, bigger than murder. Why? Because the 'mental habit' led to it.
Your brain is in the habit of waking you up, making you walk, making your thoughts into specific words, deciding what you will eat, worrying about things, judging appearances, and other things most people hardly think about, like speeding or going through that red light.
Anyways, yeah, the brain is highly plastic, thinking makes it more rigid, thinking a lot makes the thought stay in your mind like steel. Once you decide to think about something else for a while, depending on the (re/de)generation cycle in your brain, the strong thoughts will soften and loosen.
Some people simply have very healthy brains, they either create really strong new thoughts, or their old thoughts soften quickly from disuse. Just as with any skill, do not fool yourself into believeing that it is so simple for everyone. For instance, some people are scrawny non-muscular and more technically minded all of their lives, some are more the muscular manual labor types.