A lesson learnt from the dark days of the Troubles
For most people in our cities who remember the Troubles, their most common encounter with the danger and the drabness of those times was probably a traffic jam.
The greatest weapon the paramilitaries had was in their power to impose gridlock on Belfast.
An explosion or a blast of gunfire might kill a few but the congestion that followed a bomb alert and the security cordon would impact on nearly everybody.
And this was not a minor inconvenience set against the real grief of the injured and the bereaved; it was truly horrible, though the scale and incidence of it is not recorded in the history books and the tallies of the dead.
The IRA made a speciality out of messing up Christmas.
It would plant a real bomb to gain credibility for the threats and scares that would follow, and then with a few phonecalls they'd imprison us for hours in our cars on dark winter evenings.
In those days you could never promise to be anywhere on time. All you could be sure of was the tailbacks at checkpoints and the helicopter overhead.
So the dissidents have learnt that much; that they can foul up the lives of thousands of us at a time with a package on the Westlink.
And even when no one is killed the accumulated anxiety and despair in a snarled-up city is immeasurable.
Meetings missed. Children not collected or delivered.
People stuck in cars when they need a toilet or medication that's at home.
At least now there are mobile phones and we can phone ahead to cancel the hospital appointment, the job interview, the meeting for coffee, the private assignation.
But still there is the frustration, perhaps magnified for these delays not being expected any more.
If the dissidents want to tote up their achievement in Belfast yesterday they have but to remember the desperation and discomfort of being stuck in a car, perhaps with an anxious child facing the first day at a new school, then multiply that exasperation by thousands.
And if they want to know how much contempt they have reaped for their pointless endeavours, well the calulation is much the same.
As is the answer: tons of it.