Do you buy games after pirating them?

[Tackhisis]

a copy of a digital product which is virtually an unlimited market.

Digital products have a limited audience, and therefore a limited number of sales. When people steal that product, the chance of a sale is forever lost.

[Triggered Fridgekin]

When people steal that product, the chance of a sale is forever lost.

You're exactly right. There's no way to accurately quantify how much piracy affects sales because of this chance. Chances are they might treat it as a demo which can lead to an immediate purchase, chances are they might enjoy it now but are strapped for cash and will wait till it goes on deep sale at a later date or chances are they just didn't want it in the first place.