Do you think a patient's mindset is partially responsible for them dying sooner rather than later when given a prognosis?

This is a hypothetical scenario. It’s based off the fact that not all prognosis’s are accurate. I’m just curious as to your thoughts about this theory/idea of one patient’s situation.

Here’s the scenario: A patient is told they only have 6 months left to live. However, the prognosis is inaccurate and in reality, he has triple the time left, but unfortunately neither he nor the doctors know that. Since he was told that he only has around 6 months left, once that time nears, he automatically thinks he is going to die. Because of this mindset, could he actually die sooner rather than when his time is actually up, if he didn’t mentally/psychologically have these thoughts? Do these thoughts of, “I’m going to die any day now” make a difference? Does he have the ability to psychologically be partially responsible for his death around the time of the prognosis for the simple fact that that’s when he thinks he is going to die? Essentially, what I’m getting at, is that he begins to mentally shut down, which causes him to physically shut down much faster because perhaps he trained his brain to think that when the six months were up, he was going to die. I’m not saying the mind is solely responsible for this, but that it could possibly be one component to a patient’s deterioration over time sooner rather than later.
And later would be the time he would actually have left if he didn’t believe he was absolutely and positively going to die at the time of his prognosis.

I was having this conversation with a friend and we were talking about how some people can train themselves and their mind to wake up every morning at the exact same time without the use of an alarm clock. Which brought us to the topic above about people who are terminally ill.

The mind is a powerful thing.

If you think this is possible, does it change how you view doctor’s giving patients a prognosis?

What are your thoughts?