Should you assume the worst?

I remember a meme:

Me, when I notice the slighest change in someone's energy towards me... - In conclusion, sorry I bothered you with my existence.

I have always heard that you should give people the benefit of the doubt. Just because someone is rude to you, or you have an awkward experience with someone one time doesn't mean you have to write them off. It probably doesn't have anything to do with you, they were probably just off that day.

At the same time, I have also heard people say that you should take the hint. "If someone is reading, or listening to music, then it is an obvious signal that they don't want to be spoken to."

Like I have always heard that you have to have faith in people, and trust them. When you hear rumours about someone, you should never engage them, and defend them as much as you can.

But sometimes the rumours are true, and trusting them just makes you look stupid. You might have suspicions, but you just dismissed them as "negative thoughts" every time.

Where do you draw the line?