Executive Meddling: The reason this movie was directed and billed as a psychological thriller rather than a superhero origin story as Shyamalan originally intended. Arguably, this resulted in a more interesting and unique film.
What Could Have Been: The Unbreakable Trilogy. However, not being such a success, it's just a stand alone story. M. Night has said he is waiting for the right script, then he will beg Disney to make the sequel.