When two rules touch the same campaign

The moment an account has more than three rules, an unavoidable question appears: what happens when two rules touch the same campaign at the same time? Most teams ask it after the first collision — a campaign whose budget was raised in the morning and paused at noon.

It is tempting to look for the answer in ordering: “run this rule first, then the other one”. But order is not a solution, it is a way of making the collision invisible. The day the order changes, the behaviour changes, and nobody knows why.

A collision is really a design error

If two rules do two different things to the same campaign at the same threshold, there is an unmade decision underneath: at this threshold, is this campaign scaled or stopped? Instead of making that decision, the two rules have split it in half. The right fix is not to order the rules but to separate their conditions.

• Add “and cost is below target” to the scaling rule, so increases apply only to healthy campaigns.
• Add “and the same has been true for three days” to the pausing rule, so a single bad day does not close a campaign.
• Make sure you can read every rule that touches a given campaign in one place; if you cannot see who touches what, you cannot see the collision either.

When conditions cannot be separated, let the action decide

Some collisions are legitimate. If one rule is raising a budget while another brakes because a spend cap is close, both are working correctly. In that case the winner is not whichever runs first but whichever is PROTECTIVE: pausing beats raising, capping beats scaling.

A rule colliding with itself

A less discussed case: a rule runs again before it can see the effect of its previous run. The budget was raised, the campaign has not reacted yet, the rule looks again and finds the same condition still true. Three runs later the budget has doubled. The remedy is a cooldown after a rule’s own change.

Seeing the collision in advance

There is one question to ask when writing a new rule: which other rules touch the campaigns this one will touch? If you do not know, the rule is not ready to go live. Suggestion mode helps here too — two colliding rules in suggestion mode do not overwrite each other’s proposals; both are visible and the decision stays with you.