Bring me no more reports; let them fly all:
Till Birnam wood remove to Dunsinane,
I cannot taint with fear. What’s the boy Malcolm?
Was he not born of woman? The spirits that know
All mortal consequences have pronounced me thus:
“Fear not, Macbeth; no man that’s born of woman
Shall e’er have power upon thee.” Then fly, false thanes,
And mingle with the English epicures:
The mind I sway by and the heart I bear
Shall never sag with doubt nor shake with fear.

– William Shakespeare

Macbeth, Act 5, Scene 3. A brazen Macbeth is dismissive of reports of an army of thousands led by the “boy Malcolm” about to attack him. Using a bird metaphor, he says of the disloyal Scottish thanes who have joined up with the self-indulgent English – “Let them all fly…fly, false thanes.”
Isolated, abandoned and alone though he may be, Macbeth is unafraid and self-assured and determined to hold onto power. He remains sure of his invincibility in battle because of the Witches’ prophecy, which he quotes. His delusional state has given him a false self of security, believing that supernatural powers and fate are on his side. Little does he know that he will meet his end at the hands of Macduff, who was born by Caesarean section. If not certifiably insane, Macbeth is certainly acting crazy as evidenced by his obsession with the Witches’ prophecies, his self-deception and belief in his own invincibility.