Let's say you're in a crowded cafeteria, and you buy a cup of tea. And as you're about to sit down you see your friend way across the room. So you put the tea down and walk across the room and talk to your friend for a few minutes. Now, coming back to your tea, are you just going to pick it up and drink it? Remember, this is a crowded place and you've just left your tea unattended for several minutes. You've given anybody in that room access to your tea.