Take a look at this simplified version of the illusion,
where I magically turn five colored lines into six:
The "twelve man / thirteen man brain teaser" operates on exactly the same principle, although it's cleverly convoluted to make it seem as though there's more going on. Notice, for instance, that, on average, the men in the second picture are shorter than the men in the first, as is the case with the lines above.
Still not seeing it?
Then see my final page.