I didn’t take the item out of the store. How can I be charged with theft?

The Crown must establish that when the item was taken by you, it was done with the intention to deprive the owner of it (either temporarily or permanently) and that it was done deliberately when you had no legal right to take it for yourself. A theft may be defended by raising a reasonable doubt on the basis of a mistake being made (either by the store in believing you were stealing the item, or by you forgetting to pay for the item for a specific reason).