Say you're studying for a big exam and you're scheduling out how long you'll spend for each chapter. Even after doing a bit of research and hearing from others how long certain chapters take, what do you do if you get stuck on a chapter because you find it harder? Do you just study it a bit, move on, and come back to it later if you couldn't figure it out? It's hard to predict which material you will have trouble with.
Issues with Creating Study Schedules