Lunirich Edict
Running like a rabbit, giving threats, and fawning, or many prefer to say bootlicking is commonly used for survival but are in fact powerful tools, they cover the three main emotions in dealing with a leader or a powerful figure.
Each of these methods is effective in its own way and has a similar outcome to another.
Anger, caution, and pride are the emotions that are mainly possessed by powerful figures, Ian knows of these methods that saved him from the wrath of King Baralt and other powerful figures that he encountered in his life.
But in the face of Rex, he had to resort to using all of them but nevertheless still failed.
Rex has all of those personalities but he also embodies the all-powerful emotion of hatred, and in the face of absolute power Ian doesn't have a chance to do anything. What Ian lacks the most is information regarding Rex.
If he has some information then he could've polished the methods he used earlier.