The “be all and end all” is the final or most critical element of something. For example, someone might say “her performance at the debate will be the be all and end all in her campaign,” or “he acts as though racing is the be all and end all.” This turn of phrase is also sometimes written as the “be-all and end-all.”
This phrase originates in the Shakespeare play Macbeth. It comes up in a speech made by the title character as he considers assassinating a rival, arguing that if the assassination is successful, “this blow might be the be-all and the end-all—here.” As you can see, in Macbeth, it is “the be all and the end all,” and for reasons unknown, “the” has been dropped over time, perhaps because it made the phrase somewhat clumsy in spoken speech.
When people talk about the be all and end all, they are referring to the absolutely critical element, and often to something which will determine an outcome. It could be considered the final piece of the puzzle, or the quintessential aspect of a situation. Because this part is so important, it tends to be taken extremely seriously, and people who are not aware of the importance may be confused about why it is being regarded with such respect.
This term is also sometimes used disparagingly to refer to a person or event which is not important. In this sense, it is used sarcastically, with the speaker obviously meaning the exact opposite.
Many people experience critical turning points in their lives that could be considered a be all and end all, such as college applications, job interviews, and so forth. Sometimes, these events seem less important in retrospect than they do at the time, thanks to the benefit of hindsight and perspective. At other times, people regard these events as extremely crucial turning points for the rest of their lives.
When facing a be all and end all, it is important to try and keep a level head. These situations can be stressful or tense, because it may feel like one's entire life is on the line. However, one can only do so much, even when faced with a critical life event, and it is often easier to accomplish major life goals when one is not in a state of fear or panic. It can help to think of similar events which have been navigated successfully, even if such events were not on the same scale of importance.