It's wrong to obtain merchandise without paying for it.
Joss is shopping for groceries and opens a package of cookies and starts eating as he shops.
Joss wants to eat something because he's hungry.
Joss finishes the cookies, and gives the empty wrapper to the cashier to scan as he checks out.
Joss finishes the cookies and throws the empty package into a trash can before checking out.
The security guard sees Joss pay for the cookies he ate, and doesn't need to take any action.
A security guard sees him discard the wrapper, and there's a big scene at the checkout lanes; Joss can't shop there any more.