Roderigo is a very self-conscious guy especially after being rejected by Brabantio every time he asks to marry Desdemona. Roderigo has been hopelessly in love with Desdemona for a very long time, and he showers her with expenses gifts, hoping to get her attention, ending up empty handed because money cannot buy love.

Roderigo being self-conscious came to Iago's advantage. In the play, every man in Othello basically has a lady companion besides Roderigo. This hurts Roderigo's pride because everyone who is considered important isn't alone. Like a King has to have a Queen, a man must have a wife or a companion. 



Roderigo is very self-conscious because nobody treats him with respect (e.g. Brabantio, Iago...). Roderigo is also self-conscious because he tried so hard to win over Desdemona and Othello didn't try at all, and she fell hopelessly in love with him; this made Roderigo feel so self-conscious. Iago made Roderigo feel like if he listened to Iago, a smart, married man, he will end up like him and Iago thought that bringing down Roderigo's self-esteem will help him get Roderigo to obey him. In the real world,"The manipulator will try to wear down your self esteem so that you will become dependent on him/her."(SetFree)

In court, Othello said to the Duke, Brabantio, and the Senate:

"Her father loved me, oft invited me, still questioned me the story of my life from year to year.--These things to hear would Desdemona seriously incline. But still the house affairs would draw her hence, she’d come again, and with a greedy ear devour up my discourse, which I, observing, took once a pliant hour and found good means to draw from her a prayer of earnest heart --she had something heard but not intentively. I did consent, and often did beguile her of her tears--She gave me for my pains a world of sighs. She swore, in faith,--She wished she had not heard it, yet she wished that heaven had made her such a man. She thanked me and bade me, if I had a friend that loved her, I should but teach him how to tell my story and that would woo her. Upon this hint I spake. She loved me for the dangers I had passed,

And I loved her that she did pity them. This only is the witchcraft I have used. Here comes the lady. Let her witness it." (A.1,S.3,P.38-40)

Here Othello is explaining to the "jury" that he did not use any witchcraft on Desdemona, and she fell for him from listening to the stories he used to tell her Father. She'd tell Othello how if one of his friends loved her and were to tell her a story like his, that wouldwin her over. Desdemona then confirms Othello's story by saying:

"My noble father, I do perceive here a divided duty. To you I am bound for life and education. My life and education both do learn me how to respect you. You are the lord of duty. I am hitherto your daughter. But here’s my husband. And so much duty as my mother showed to you, preferring you before her father, so much I challenge that I may profess due to the Moor my lord."(A.1,S.3,P.40)

If I were to be deeply in love with somebody who doesn't pay any attention to me, and keeps rejecting me, I would be self-conscious and furious at the fact that they fell in love with someone else. Also, Othello didn't even try to win Desdemona's heart yet she fell for him. Roderigo, on the other hand, tried so hard to win her heart. This must have made Roderigo feel like he was never good enough for her, and that Othello is way better than him, making him want to get rid of Othello, and drown himself. 

In the real world, suicide rates, eating disorders, and self harm have increased rapidly because some people don't feel like they live up to peoples expectations, and feel very self conscious about themselves because of past experience with people who did not accept them the way they are (making them feel not good enough).

In conclusion, it was so easy for Iago to manipulate Roderigo because of his strong love for Desdemona and continuous rejection, his lack of intelligence causing him to make the same mistakes constantly after each other not knowing why nor understanding why, and his self-consciousness and jealousy of Othello feeling like he is way better than him because Desdemona chose him.

References

Shakespeare, William. Othello. Thomas Walkley, 1622. Print.

Markham, Samantha, Character Analysis of Iago. 01/02/09
    Suite101, <http://suite101.com/article/character-analysis-of-iago-a157049>

Scott. Othello Scene Play. StudyMode.com. 02/12
    <http://www.studymode.com/essays/Othello-Scene-Play-91682.html>

Deepak, Chopra, What is Manipulation and How do I Recognize it?
     <http://www.sharecare.com/user/deepak-chopra>

Set Free, The Manipulator's Behavior Being Defined. 09/16/09
     <http://setfree0408.blogspot.ca/2009/09/manipulators-behavior-defined.html>