It's tough because the 100 card count makes you feel like you've got unlimited options. Until you add in lands. Mana rocks. The must includes like Sol Ring. Oh yeah, don't forgot that the commander and the partner count to the limit, so you've got to cut down 2 more.

I thought the hard part would be finding enough cards to fit whatever deck I'm building, turns out it's picking which cards makes the pick.

A lot of my final cuts are cards that I thought would be cool, but they barely match my overall strategy in the deck. Like if I have a card that gives me counters when I gain life because I also have a card that gives me life when I make tokens. Cool, I make lots of tokens in my token deck. I only have that one lifegain card though. I'll never draw both in the same game so might as well cut it.