Paul's memory, or lack of one, drives most of Tangerine's suspense and action. Our past is so important to our identity that missing any part of it creates a terrible void. And no one likes having a big chunk of empty brain in their head. Right, zombies? But Paul isn't the only one with amnesia. No one wants to talk about or remember Mike's death, either, until months later, when they finally plant a tree in his honor. And the new inhabitants have even mostly forgotten Tangerine's past as the tangerine capital of the world. Even though its name is Tangerine. How's that for blindness?
Remembering his own past, on his own, is more meaningful for Paul than if he had just been told what happened to him.
Paul's past affects every single thing that he ever does.