I always found it interesting that they put all this effort into getting Fisher to do something (can't remember exactly what) for Saito, and this whole complicated plot goes into planting the Inception in Fisher's dream, while he basically spends the whole dream trying to save Saito's life. He will wake up with his feelings about Saito affected even if they fail to implant the idea. He almost "incepts" himself, and I think it hints that this "impossible" thing has probably been done accidentally before. Like, if someone's mental security system goes off when you get in and you leave, they'll be slightly wary of you in person without knowing why.