My sister was looking for her credit card that she left in the bedroom. I wanted something at the store, I did not have any money, so I borrowed her card.
I was helping my sister to look for her card, even though I knew she wasn't going to find it 
user
That is nice from you. What card is it?
assistant
It was her credit card, I borrowed it without telling her
user
Why did you do that?
assistant
I wanted to purchase something and I did not have any money, so I used her card.
user