Note to Hamlet, 1.4.36-38: "The dram of eale / Doth all the noble substance often dout / To his own scandal"

This is a "crux," a passage which is open to various interpretations because there has been some kind of error in the printing. In this case, "eale" isn't a word, and "of a doubt" doesn't make any sense in this context, so "eale" is usually changed to "evil," and "of a doubt" is changed to "often dout," meaning "often extinguish."

With these changes, the sentence means, "A person's small fault often extinguishes (in public opinion) all of that person's praiseworthy qualities, resulting in the shame of those praiseworthy qualities, (and the shame of the person who has them)."

This meaning fits well with what Hamlet has said just previously.