How the Bias Forms
A buyer sees a display ad (no click). Three days later, they see a Reels ad (click, no purchase). Five days later, they search the brand on Google (click, purchase). Last-click says Google made the sale. Display and Reels are ignored.
What Happens When You Trust Last-Click
You cut display and Reels budget because they 'do nothing.' The acquisition pipeline dries up, brand search loses its pull, and sales drop. Three months later you cut brand search too because ROAS has fallen. The spiral has begun.
A brand using last-click reports cut ToF budget by 60%. Three months later, brand search volume had halved and sales collapsed. Recovery took 12 months.
How to Eliminate the Bias
Multi-touch setup with custom events. Linear or time-decay attribution model. Track channel contributions weekly. Base budget allocation on multi-touch, not last-click. Setup effort is 4 to 6 weeks; ROI is visible within the first quarter.
„Last-click is not wrong; it is incomplete. Treating it as truth burns 32% of your budget.”