The same way the Big Mac shrinks in time...

Basically as a vendor you have to sell as many units as you possibly can. Ideally, the buyer acquires your product and it breaks down as they exit your store. They come back and buy again. The cycle continues as they lack critical thinking to understand the causation.

Inflation is indirectly the cause because it injects more money, diluting the existent supply. Since money means somebody actually put in the work to create value in the first place, putting in more artificial money means that nonexistent work floods the market competing with actual work.