If you’re on the edge of a cliff with a snake, you’re unlucky. You’re hanging off the edge of this cliff and you can’t pull yourself back up when you notice a snake approaching your fingers. The snake looks like it’s gonna bite you. How unlucky.
Even though you’re so unlucky, you decide to take your chances and let go of the cliff. Amazingly, a yak (やく) runs below you and catches you as you fall. Saved by the yak!