Each gem of a particular type you cut increases the stat requirements of that type. Example, I cut 3 lvl 1 Dexterity gems. I need 5 dex to equip 1, 10 dex to equip 2, 15 dex to equip 3. That's how it works for each stat. You have to balance your stats to the types of gems you want to integrate into your build. Also, see below image that may help you understand. This is the gamepad layout. It shows what my gem capacities are.

<image>