It is only later in Act III, iv that he completely loses his rationality, and evil culminates to its peak. Hence, the change outlined is very subtle.
"Macbeth" is a tragic story about the fatal flaw of an honourable Thane who is defiled by his own ambition. The two soliloquies in Act I, vii, and Act III, i, Shakespeare conveys the development in Macbeth's character into a power-hungry tyrant. Against others, he may have been the "brave Macbeth", but when the enemy was the man himself, he never proved to be a worthy opponent. It seems that ambition has been given a bad reputation, for the character of Macbeth, due to its defects, was never the right medium to accommodate and, unlike that of Banquo, suppress its malice for the benefit of the greater good.
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