My mom’s had people try to tell her that she only thinks she has type 1 diabetes because the doctors told her she does, and if she stopped believing them, her pancreas would start working again.

I was just reading this article about a mathematical understanding of closed time-like curves.

In essence, the argument is that time travel to the part is possible with a degree of free will, but you would not be allowed to alter the part in such a way as to remove the motivation for traveling back in time. E.g., it would be like Futurama where Fry kills his grandfather, but he impregnates his grandmother, this allowing himself to be born. The idea is that the timeline would correct itself and ensure that your future self will always return to the past.