I don't understand why there is a whole little science to this with so many YouTube videos [1]. There is the weight of the rider plus clothes etc. There is the PSI in the chamber. There is a table on the fork to help you with a reasonable value. After that, adjust up or down at discretion. What am I missing?

[1] e.g., https://www.youtube.com/watch?v=CYjoTM8asKA