Answer:
In Shakespeare's "Hamlet," the protagonist claims that some men are born with a "vicious mole of nature in them," meaning that one small defect (like drinking) can wash away someone's achievements and make people look down on somebody in spite of that person's talent and kindness.
Similarly, Hamlet mentions "The dram of evil" to refer to a small amount of usually whiskey. In that respect, he indicates that a small amount of evil or a flaw can make the admirable or good seem flawed or bad.