Remember the last time you made a purchase? You clicked on an ad on Google, visited a website, saw the product, then went to the competitors to compare prices and features, came back via Facebook ads, talked with a few friends and colleagues, talked to a salesperson, downloaded the specs… And then a few dozen other actions.
Attribution is all about measuring all of these touchpoints along the customer journey and assigning value to them. This allows you to calculate ROI and identify the touchpoints that bring value.