What is it about DOTA that is so addicting?

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I can not understand why guys can spend hours and hours in front of the computer just to play DOTA. I can't understand the concept of the game, but i find it so amusing that guys will spend more than an hour in front of their pc because they lost track of time while so engrossed with the game. Some would even forget to eat because they are so into the game. And just recently, another game called Heroes of Newhert (HON) almost similar as DOTA caught the attention of the guys again. What is it about the game that guys would even trade their time for the girlfriends in exchange of longer hours to play these games?