What's the Hardest Part of the Filmmaking Process?

The project for me started with like the thematic and the aspect of looking at beauty as a currency. There's a whole third act that I don't want to talk about because I think people really enjoy being surprised where the film goes. When it starts to narrow down and you start to decide ah this is exactly how I want it then starts to struggle of like how do I visualize this? Then I like imagining it in my head and from that point it's a struggle from every single day when you are shooting for example. The pre-production is always quite fun, but post editing can be tough too. It's about stamina really to be a director I would say.