London Underground users can pick up a free morning newspaper called Metro. The publishers of the newspaper produce enough copies for 50% of Underground passengers - travelling between 6.30am and 9.30am - to read. The true genius of this enterprise is not the paper itself, but its delivery mechanism, which takes into account the following considerations:

• The distribution system relies on the basic human instinct to pick up any piece of paper with the word 'free' on it.

• Copies are placed in neat piles at the entrances of Underground stations so they can be picked up by people at the start of their journey into work.

• Any commuters who haven't picked up a copy of Metro by this point, will notice, the moment they get on a train, that everybody is reading it and they're seized by the desire to find out what is so interesting in a newspaper that everyone appears to be reading.

Here the pure genius of the distribution system comes into play. The content of Metro is limited in such a way as to only supply enough interesting reading matter for 20 minute tube journey. As such the original owner of any copy of Metro, not assigning any value to it (as it was free) abandons it after 20 minutes or at the end of their journey. Whereupon the now insanely curious onlooker, in total disregard for normal social etiquette, will lunge across the carriage to grab the abandoned copy. By the end of the day, a relatively small number of copies of Metro have reached a massive number of the London population.