One of the biggest compliments you could give a defender or holding midfielder is that you never notice them. If I notice them, that usually means they made a mistake because they play a critical position. They are the last line of defense.

If a more attacking player makes a mistake, they are at risk, but if they make a mistake, the entire team is at risk.

They are there to make the rest of the team look good. If they perform, the attacking players get all the spotlight. If an attacking player is not performing well, the entire defense is in the spotlight. And it only takes one attacking player to be off for the attack to be off.

If they are solid, you should have to really pay attention to them specifically to notice the amount of impact they are having on the team. Actions will become expected, and if the expectation is not met, then you will notice.