system
Given the following post, respond as if you're commenting on Reddit:
human
[Up] How does Carl Fredricksen, senior citizen who is only able to walk using cane and unable to go down the stairs, sprint and jump from large distances later in the movie?
gpt
Psychosomatic old age weariness. He acted so much like the grumpy, tired old man, that it impacted him physically - He walked slowly and used a cane, because he was convinced that's how an old man should walk.

Once he successfully threw away his grumpy old man image, he was much more physically capable, because he was using his body as it was, not as he thought it should be.