You know what is a distinguishing feature of good character development? Characters should be predictable. Like an acquaintance, you should be able to tell what their reaction would be to some situation. How they would think about it, what they would say, and what they would do. Each moment when you don’t really know how they will react is an opportunity to learn more about them. If you never know, if you can’t predict anything, then it means there is no character development; the character is just a tool.
Mr Nobody, like the equally crappy Butterfly Effect from 2004, uses lack of character development to try to convince us that life is chaotic and can be totally altered by ridiculous details generating grandiose consequences. Characters end up in totally different lives, and totally different mindsets, in the tree of possible storylines. Characters are just set pieces enduring the circumstances of their storylines. I won’t take a philosophical stance on the butterfly effect philosophically speaking, but I can say for sure that I find this approach of chaos awful to watch, narratively speaking. What can you hold on to if characters are just tools? This is useless.