Nature IS out to kill you. And it will, eventually.

Plucky little fella going after an eagle like that.

Eagles, like most predators, can ill afford injury and are risk averse unless desperate. Hard to know if the fox was desperate or what the outcome might have been if he had
come up with a mouthful of eagle.
Some years ago I saw an eagle and a muskrat sitting on an ice covered lake. I thought the outcome was a certainty and stuck around to see the eagle take the rat. The eagle would lift up and hover above the rat, which would strike a defensive posture, and the eagle would return to the ice. This was repeated several times; if the eagle descended low enough the rat would even jump up at the eagle. Of course, muskrats, like most rodents, have strong jaws and sharp teeth. A bite, even from a dying muskrat, could have serious consequences for the eagle. So each time the eagle backed off the rat would move closer to the cattails along the shore. Clearly the eagle wasn’t THAT hungry. This went on for 30-40 minutes and when I left I was sure of the outcome.