“I think my girlfriend might be cheating on me, I’m going to snoop around on her phone.”
“I don’t think that’s a good idea. You know what they say: curiosity killed the cat.”
“My son burnt his hand touching the hot stove. Curiosity killed the cat.”
There is a proverb in English “Curiosity Killed the Cat” which warns someone that excessive investigation or experimenting will lead to a bad result.
In the first example the friend is warning that if the first guy looks in his girlfriend’s phone it will have a bad result (maybe his girlfriend will get angry).
In the second example the father is saying that his son was too curious about the stove and touched it to see what would happen, which gave a bad result.
This proverb comes from the idea of a curious cat, but that its inquisitiveness leads to its death. Try to picture a cat that is curious about the edge of a rooftop, goes to the edge to look over, and falls off the building.
We use this proverb generally to warn people not to try something foolish or not to ask certain questions.