What makes you not a sheep?

I've just had a thought of the Jews during the holocaust being murdered by the millions not fighting back even when they were forced to dig a hold for their friends and eventually themselves. It's a complete sheep mentality if not worse. Sheep will stand around while you slaughter their mother and everyone eventually you'll end up killing them. Hence the insult you're a sheep.

So my question is how do you know you're not a sheep going with the flow of what is around you?