When you look through someone, you see the person, but pretend not to. As far as you are concerned he is not there, he doesn’t exist. When you see through someone, you are able to figure out what the individual is up to. In other words, you understand what he is planning to do; what his intentions are even though the individual is trying his best to hide them.
*Harish was able to see through Narender’s scheme right from the beginning.