Seriously though, it's hard to track success.
If I'm showing an ad wanting people to rush out and buy sneakers... it's rare that it will hit the right person at the right spot in their sneaker purchase decision journey.
But what I want is to bombard them with information so that when they are ready to buy sneakers, they think positively of the sneakers I am selling.
I don't care if they don't follow a perfect path on my site... if they click around and click off... they most likely aren't going to click and buy on the spot. I'm OK with this.
How do I know if my advertising is working? Well... tracking users is one way, but just asking users is something a lot of stores don't bother with. A simple "how did you hear about us?" or hit them up with a customer satisfaction survey after the purchase with a few questions -- incentivized with a coupon. You'll get some great metrics that will help you understand if you marketing budget is being well-spent.