This post is going to break two rules.
There was a point while he was writing Fight Club where Chuck Palahniuk came to realise that the two characters – the narrator and Tyler – were the same. It wasn’t a twist he’d thought of before writing. It wasn’t a gimmick to string the reader along. He was writing a damning commentary on masculinity as he saw it in the mid-1990s.
As for the split personality aspect, I assume that it hit him as hard as it hit the rest of us.
It was in the writing process where these ideas came together so strongly and delivered Palahniuk’s powerful novel. Giving up that experience of being deep in the writing process – as frustrating a process it can be sometimes – robs you of such powerful moments. It takes away so much other richness that can only be brought out by doing the writing.
Invest the energy. Do the work – the process is the point.