Jump to conclusions

Meaning/Usage: Making a conclusion without having all the details

Explanation: If you need five pieces of information to come to a conclusion, jumping (or skipping) over 3 of them will cause you to make an incorrect conclusion. This term is often used when an incorrect conclusion is made by someone who didn't have all the information.

"I incorrectly blamed Jeff for breaking my phone. I shouldn't have jumped to conclusions."
"I thought you took my book. I shouldn't have accused you. I jumped to conclusions."
"Will you stop jumping to conclusions. You should get all the facts before you make any decisions."

A: "I'm so mad at Jake. I think he told my girlfriend that I was on a date."
B: "What makes you think Jake told her?"
A: "Because he's like that."
B: "He sometimes does stupid things, but you shouldn't jump to conclusions."