I like the analysis of the quote that explains it as a message of the morality within human actions. The progression of language in the quote parallels the descent of human action. To "dare" implies a level of thought that could only be conceived, but never done. This could act as the first step in embracing immoral or unethical actions. What individuals "may" do helps to explore the idea that thought has translated into action, and some line from pure thought has been crossed. The final part of doing what is done "daily" and "not knowing what they do" helps to underscore the idea that immoral or unethical actions are undertaken without much in the way of consequence or thought about implications. In the progression or devolution of action through language, one can trace nearly any act that seeks to break the bonds between individuals or the severance of connection to the morally righteous and upstanding path.
This quote is spoken by Claudio during his wedding ceremony to Hero in Much Ado About Nothing. Claudio is angry because he erroneously believes that Hero has been unfaithful and unchaste. This is not true, but part of an evil scheme by the villain Don John. The Friar has just asked if anyone knows of any "impediments" why Hero and Claudio should not be married. Claudio asks Hero if she knows of any, she replies in the negative, but Claudio thinks she is lying. Claudio then utters this quote, which, I believe, is a reaction against what he thinks are lies, not only by Hero, but by her father and everyone else that states there are no impediments to their marriage. He believes everyone is lying to him and he is frustrated. He believes he has been duped.
The quote can apply to life in general because all men are sinners and they commit sins on a daily basis. They cheat, they lie, they steal - they "do" all manner of things that are deceitful, evil and harmful. They are so evil they sometimes don’t even know what they are doing. This is reminiscent of Jesus’ words on the cross, “Forgive them, Father, for they know not what they do.”
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Claudio says this as he's rejecting Hero at the altar. His impression is that she wronged him, and with her virginity gone, she is repulsive to him. So, to Claudio, he was prepared to marry Hero not knowing that she had been with someone else. This of course is not true, Claudio having been tricked by Don John, so the quote's meaning is underscored by this dual-misrepresentation of reality.
Claudio had been as (or more) infatuated with the idea of Hero's purity than with Hero herself. He was also tricked by his own senses (witnessing the ruse where he thought Hero was with another man). So, Claudio 1) brainwashed himself into loving a trait about Hero, rather than Hero herself, and 2) was brainwashed by Don John into believing another falsehood.
Applied to life in general, I think the quote refers to the fallibility of people. We are all capable of making mistakes, whether being fooled by others or even fooling ourselves. Claudio, being immature and inexperienced, is guilty of both. Especially when emotions are involved, we are more susceptible to these types of things, going by gut reactions rather than rational thought. What we "can" do, "might" do, everyday, even if we don't "know" for sure if we're right: that is a dangerous method. This play is a comedy, but Claudio for one, was almost killed because so "much" was made about "gossip" and fictitious gossip is essentially nothing, but can be used in destructive ways.