You bought a lottery ticket. You mention it to your roommate. She asks if you think you're going to win. Of course you don't think so, but you do have some small hope. You say this.
Well, you never know...
This phrase means that there's a small chance that something could happen.
Use this to talk about something that probably won't happen, but possibly could.
A common way to use "You never know..." is to say that something might be useful in the future. For example:
A: Do you want to keep this? We don't use it anymore.
B: Yeah, let's keep it. You never know...
One of the many ways to use "Well" at the beginning of a sentence is to defend yourself. When someone has attacked your actions or something that you said, you can say "Well" before you explain yourself.
A: You never do the dishes!
B: Well, that's because I don't use as many dishes as you.
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