Find the item you want to steal. Now, use the right analog stick ('click it') to pick up the desired item.

Simply carry it to where your hidden, and steal. Simple!

Also, save before you pickpocket (in a crouched position-hidden or not - it doesn't matter...)

Go to settings: Change to 'Very Easy.' Pickpocket desired item. Reload the Saved Game if failed.

Try until you succeed.