One time I was climbing trees with my friend in a forest (Assassin's Creed 3 was nearing release at the time, so me and my friend were getting into tree climbing), and when my friend went up to the top, He told me to climb on up.
I took a bit of an alternate route than he had, and the only way to get up to the top was grab a branch that was sticking out, and pull myself up. I made the stupid mistake of not checking the strength of the branch before climbing it, so I was about halfway into getting my leg over when I hear a crack, and the branch I'm holding moves.
In that moment, me and my friend had just enough time to look at each other, and that's when he chose to say, "See you on the other side, pal."
When he said that, the branch gave way, and I fell. Since we used other fallen logs to climb up, I hit every log on the way down, only like 2 or 3, nothing big.
With my quick thinking, I managed to grab hold of one, right before falling down farther, but that slowed down my fall so I was good. I landed next to a jagged log, which probably would have impaled me had I not grabbed onto the branch when I did.
Moral of the story: Test the strength of branches you're about to grab onto when you're climbing a tree.