Maybe it's just me, but I love how important players of the team, particularly defenders, that when they are injured or suspended, can easily tarnish the overall balance of the side.
Take this for example, going into my second season, I am 6 games into the league. Won 6, lost 0. 20 goals for, 0 against. Luiz picked up an injury, to which I replaced with Rudiger. In my CL match against Celtic, I lost 1-2.