The difference there - you can at least verify your ad is being shown, even if it is not a guarantee of effectiveness, and use other estimates to see how many people see it such as foot traffic or TV viewership.

I have no real way of knowing how many people see my online advertising, I just get a number and a bill, and I have to trust them. The pixel does help for visits but not views and other metrics.

> “Half the money I spend on advertising is wasted; the trouble is I don't know which half.” — John Wanamaker (1838-1922)

I used to have a retail store on a busy state hiway in a congested area. We put out a used ragged-arse flashing arrow sign that just had keywords on it or maybe a few sentences for products we sold. That worthless piece of junk printed money.

Road signs, sidewalk signs, and billboards are worth every penny.

They work.