In the Director's Cut, there is an additional scene where Evan and his mother go to see a fortune teller. She reads his palm and tells him he has no life line and no soul -- he's not meant to be here! There is also a scene where Evan's mother sits down with him and explains that she had some stillbirths before Evan was born. Evan was her miracle birth. Further evidence that Evan was not supposed to even exist! So Evan's birth must've been brought about by Evan's father changing something in the past (either intentionally, to try and rectify a miscarriage so he could have the son he wanted, or unintentionally due to some other event).

So if you have the theatrical ending, then it would mean that even though Evan was not supposed to exist, he made good in the end anyway. That's a really crap ending because it goes against his father's own harsh realisations. So the only ending that makes sense when you have the director's cut is that Evan finally comes to a similar understanding as that of his father. He realises that he was not supposed to exist anyway, so removes himself from existence as best he can by strangling himself on the umbilical chord, thereby correcting his own mistakes and some of his father's mistakes. A great ending to a great movie!