One of the difficulty options lets you have more or less skills. 5 is the lowest number of skills you can have, and you get a %increase to some stats for it, you can increase the number of skill slots you have avalible up to 10, but lose some of that % increase to stats until it's at 0% at the full 10 slots. It's entirely up to you how many skills you need at once.A question: in the menu it's possible to pick 10 active skills, but in reality I can use in battle only first 5, why?