A childhood belief about criminals

I was in a grocery store when i saw a lady 'steal' a grape. i was in a policeman stage that every boy goes through and i had these little plastic handcuffs. I took them and i said 'lady, you're under arrest.' She started to quickly walk away and i started screaming, 'theif!' the whole store was looking at her and me. In the car my mom took away my handcuffs and told me that i should never do that again. I was very upset that i couldn't save the world.