How is Othello's behavior predictable?

Othello's actions are predictable because of his personality, his position as a "moor," his role as a military man, and his experiences in battle.
Othello is an upright, honorable man and expects others to be the same. He trusts Iago, believing him to be his friend.
Othello is an African, Muslim, and/or person of color, one of few in his predominantly European, Christian, white environment. He has worked hard to succeed, including at winning Desdemona. Others envy and resent him.
Othello made his way up through the military. He understands the macho soldier world much more than women and emotions.
Othello has spent countless days in combat. Finally he can take a break, but does not really know how. Not only is he out of his element, but must try not to dwell on the war, as he will have to go back to it. Using today's mental health terminology, it might be considered that he suffers from PTSD.
https://shakespeareandbeyond.folger.edu/2017/11/03/shakespeare-post-traumatic-stress-disorder/

Othello is framed as an authoritative, honest, and brave "Moorish" general in the beginning of the play. Shakespeare introduced him in this light to show how much he has strayed from his good characteristics later on in the narrative when Othello experiences his downfall. Othello's reputation as a warrior and leader is also meant to show that all men have a weakness despite their exterior image.
The weakness that makes Othello predictable—not only to the readers or audience of the play, but to Iago, the villain of the story who manipulates Othello—is his jealousy. His jealousy is perhaps related to his self-image as a decorated warrior and a man not to be crossed.
Shakespeare has many characters in his plays who have prominent social and political statuses—like kings and generals—who have deep insecurities because they cannot fathom anyone betraying them. This predictability in Othello's characteristics allows those lesser than him to influence his psyche greatly.