dark-prince-of-clowns:

What do we know about Izaya? He loves fatty tuna, he owns a lot of cellphones and he is a light sleeper. And he also loves to play–be it a game, a part in one of his “plays” or with a heart he can stir up. He has that childish side to him, not doing too well with losing to someone, especially if it is his sworn archnemesis Shizuo Heiwajima. He is a man who wants to be in control as he observes how situations unfold, hopefully amusing him. Izaya’s characteristic claim throughout the series is that he loves humans more than anything and therefore wants to place them into a scene in which they behave out of the ordinary and exceed their limits and his expectations. He may go as far as putting himself in danger for that. Nevertheless, his love for humans appears contradictory when we see his masquerade crack, when we see how he might just be a lonely soul that is extremely insecure and afraid of proper human interaction and bonding. According to Shinra Kishitani, one of the few people who are close him and appear to be able to see through his facade:

He may seem cold-blooded, but he is more human, and his heart more brittle than anybody else, so much so that if you filled it with human love or betrayal, it would break easily, which is why, I think, he chose from the start to avoid it all, to love humanity, you understand? Not to accept, not to face it, to avoid it.

Izaya