The Barcelona metro system caught me out yesterday on my way back to the hotel. Getting from the hotel to the venue for The Server Side Java Symposium was easy, just buy a one price (very cheap) ticket and go straight there with no changes. What caused me problems was the barrier to get into the metro on the way back. I put my ticket in, the machine read it, and spat it back out. The arrows illuminated to show acceptance, but the barrier wouldn't move. I was confused. The ticket was valid and had been accepted. Why couldn't I get through? Thankfully a very nice Spanish lady set me straight by pointing out that the ticket reader was on the left of the barrier, not the right, so I was trying to go through the wrong barrier. Duh! According to the article on Wikipedia 8-15% of the general population are left handed so why put the ticket reader on the left? Of course you could argue that people will be holding bags, etc in the right hand so the left side makes sense. What really doesn't make sense to me is why it's not consistent. If it was always on the right or always on the left that would be sensible, but apparently randomly choosing a side is bound to cause problems.