Final answer:
Donalbain and Malcolm flee Scotland after the murder of their father, King Duncan, fearing for their own lives. Their departure is a response to the belief that they cannot trust even close family, as treachery is afoot. Their actions later play a significant role in the events leading to Macbeth's downfall.
Step-by-step explanation:
The belief surrounding Donalbain and Malcolm and their reason for leaving is rooted in their fear for their own safety after their father, King Duncan, is murdered. In Macbeth by William Shakespeare, Donalbain and Malcolm express their apprehension that they may be the next targets. After the murder of Duncan, they decide to flee Scotland to avoid the same fate. Donalbain suggests to Malcolm, "Where we are, There's daggers in men's smiles: the near in blood, The nearer bloody", indicating that they cannot trust anyone, not even those who are closest to them by blood, as they may harbor intentions to kill.
Malcolm flees to England and Donalbain to Ireland, aiming to protect themselves and possibly muster support against the usurper, Macbeth. Their departure is considered by some as an act of cowardice, while others view it as a strategic retreat. Ultimately, their decision to leave sets the stage for the subsequent events that lead to Macbeth's downfall and restoration of the throne to its rightful heir, Malcolm.