The original question had to be edited. I would suggest that Othello's downfall is quite convincing. Othello's downfall is caused by his own insecurity. It is doubt in himself, in Desdemona, and in the world around him that plays a major role in Othello's downfall. This is shown in a convincing manner.
Shakespeare shows this demise to be incremental as the play progresses. For Othello, the lingering doubts of himself as an "insider" from one who is an "outsider" become evident. These are what help to fuel his downfall. Jealousy replaces his confidence. Where there was certainty, there is now insecurity. I think that this is where his downfall becomes convincing. Shakespeare shows how the most lauded of individuals can become "undone" through their own sense of unchecked doubt and insecurity. It is unravelling for Othello to be immersed in a condition where he constantly undergoes self- doubt and uncertainty. From a man who could fend off external armies and threats from abroad, Othello becomes a man whose worst enemy is himself. This is shown in a convincing manner, taking a toll on both himself and Desdemona.