In Macbeth the title character becomes evil and more evil by degrees until he is completely shrouded in a hell. When mammals taste blood; they gradually get more and more vicious until there’s no other choice but to end the viciousness. Once Macbeth tastes the blood of King Duncan (metaphorically) he can’t stop; that blood aldulterates his state of mind and he becomes restless, guilty and ripe for further evil. As someone states:
“Unnatural deeds do breed unnatural troubles.”
From the murder of King Duncan on, one misdeed leads to another with death as its only probable outcome.
A good metaphor for Macbeth’s situation; he’s like a gambler who’s had an incredible winning streak one day and comes back days later (expecting things to go the same way). After he loses what he has won and is left with his mere principal money, he has to decide whether to play it safe and realize you can’t win ’em all, or go for broke and leave his horns without a case, but HE CAN’T STOP!. He’s gotten a taste and will inevitably lose all.
When Macbeth attains the title of Thane of Cawdor he’s won a great deal, but when his murderous ways begin to take hold, he becomes resigned to his fate.
“I am in blood stepped in so far that, should I wade no more, returning were as tedious as go o’er.”
He lacks the temperance to reform. His initial status of a noble warrior is tainted by the promising success of the weird sisters and dominoes into his demise.