In Shakespeare's play Macbeth, Macbeth and Banquo have very different reactions to the visitation of the three witches.
Macbeth is entranced by what the witches have told him. He becomes preoccupied with imagining what the weird sisters' words might ultimately mean to him. Becoming Thane of Cawdor would be nice, but becoming King is unimaginable—or has been up to this point.
Banquo, also a great warrior and Macbeth's good friend, is very different. He is cautious with regard to the witches' words: he asks for his prediction, but tells them he does not fear them and he will not beg. He expresses no deep longing, but perhaps only curiosity.
When the witches' first prophecy comes true, Banquo is shocked:
What, can the Devil speak true?
(Elizabethans believed the Devil could not speak words that were true.) Banquo is cautious and tells Macbeth he should be cautious as well.
...'Tis strange; / And oftentimes to win us to our harm, / The instruments of darkness tell us truths, / Win us with honest trifles, to betray's / In deepest consequence.
The words mean that sometimes evil can trick us with something small, like getting the title to Cawdor, but then lead us do something awful later, because we believed the first little prediction that came true.
Macbeth has little doubt after the witches' predictions, especially when he receives his new title, but Banquo exercises caution and counsels Macbeth to do the same.