This is a fairly legitimate question, and there are three parts to the answer: Synchronic scholarship, poetics, and dramatic/ literary history. First, the Elizabethan age was a time of cultural expansion, global exploration, and linguistic maturation. In other words, the English language was having a growth spurt – Shakespeare alone invented hundreds of words, many Latin- or Greek-based, some transformed from common slang, some purely created out of his imagination. Because Shakespeare’s work was in print, these new words and phrases began to gain a foothold in the language. Secondly, because the plays (as well as the sonnets) were in figurative (metaphors, rhymes, alliteration, colorful imagery, etc.) language, meant to be spoken, they were easily adopted for daily use (just as slang today catches on when used in public media) and easy to remember and re-use when new conversational occasions arose; finally, Shakespeare’s work has been constantly restaged and reprinted though the five centuries, without any large gaps in its popularity. The combination – new phrases rich with meaning on several layers, easy to remember and recite, kept alive in changing societies – has turned many of Shakespeare’s lines into convenient shortcuts for expressing even complex ideas. Your example, “to be or not to be,” encapsulates the whole dilemma of life – not just whether or not to commit suicide (its most obvious meaning), but the whole philosophy of why we make daily efforts, why we make choices at all – why we choose to give value to life, our own or anyone else’s. It begins Hamlet’s inquiry into action or inaction. So whenever the subject comes up in conversation, the easy, rhythmic phrase springs to our lips.