Controller

The main thing for this role is smoke
Smokes are needed to protect us and cover us while we are busy with something else.

The controller is also sometimes independent (if everything is calculated and played smart xD ).
Sometimes it's a good sentinel

If I don't do what I'm supposed to do then :
The game will be much more difficult and we will not be able to play strategically and we will not be able to enter cover all the points at the same time or defend.( without smokes )
We also won't be able to block or play for time
The game will be straightforward and always readable (without smokes)
The team will not be able to plant the spike since im almost always with the spike (expect icebox)

Since I am a controller, I can understand that I am doing my role well if :
Smokes, wall , flash , everything by right timing
My teammates are happy
we discussed with a teammate how we would play together before the enemy came out