What is the most obvious mistake you think people do?

For me it's the "I'm constantly getting ganked, jgl diff." people.

These guys constantly overextend, don't ward and then blame someone else when they get ganked and it honestly melts my brain. You'll even ward for them, ping enemy jgl ganking, ping for them to back but they just can't seem to grasp the concept that if the enemy jungler is sitting your lane, it's probably because your an easy target. If you've gone 0/5 in 10min, your probably doing something wrong.

What's everyone elses oddly common while being painfully obvious mistake?