You don't even have to do anything wrong while on stun duty.
All it needs is some stupid dps that spams their stun too and triggers DR.

All in short: I really hope SE steps up their 2 tank fights. So far its boring bullshit. You either are stunbot. Or only there to pick adds twice a fight..or even completly useless since people take only 1 tank to titan...
I am happy I haven't seen coil yet so there is little hope it will be better...