I remember as a teen studying Macbeth thinking that the quoted text was the most rational thing Macbeth says in the whole play. Why doesn't he take his own advice? (There wouldn't have been much drama left).
I you believe that X outcome is will necessarily occur, as a matter of destiny or fate, why engage in any action A to bring about X? Furthermore, isn't it irrational to engage in A when it incurs some further cost (as indeed it does for Macbeth)?
This is a common leitmotif in stories concerning fate. It always makes me wonder why people, who apparently do believe in prophecies about themselves, go to all the trouble of helping to fulfill the prophecy - often with tragic consequences.
It's pretty clear that [spoiler!] things don't turn out well for Macbeth. His overall behaviour is not rational, even by the metric of achieving his own ends.
Let's imagine the play turns out somewhat differently and he gets away with his crime. Even in this scenario, he has to live with the knowledge of killing a "graceful and renowned" man.
The cost of attempting to bring about his destiny is huge: a significant risk of things spiralling out of control and a murder which must be, even from a self-interested perspective, emotionally traumatising.
The cost of waiting for things to happen 'without his stir' appears modest by contrast: perhaps waiting slightly longer to be king.
On the model of expected utility, he should heed his own advice.
I think there are parallels with Newcomb's paradox (https://en.wikipedia.org/wiki/Newcomb%27s_paradox). This trades on a similar concept: the idea of infallible (or near infallible) prediction.
What are the philosophical approaches to fate and rationality? What would they make of Macbeth's behaviour?