What does Hrothgar caution Beowulf against?

Hrothgar cautioned Beowulf against one of the most important things ... Pride

I agree with the other person - pride is something that Hrothgar cautions Beowulf against. Excessive pride (also known as hubris in Anglo-Saxon poetry) is not a desirable characteristic that a leader/warrior should have because it will lead them to their demise in the end. This is what happened to Beowulf ultimately - he thought he could defeat the dragon in his old age because of his hubris, and because of it, he died.