The idea is simple: why not leave poetry printed on business cards in cafes and other public places where thye may be found and enjoyed by people who would normally not encounter it? It is no coincidence that I had spent a long sumemer afternoon on a London underground train and found myself considering the text of one of the Poems on the Underground a few days beforehand. But my aim was different: to make the case for brief, unpretentious, poems which were rooted on authentic human experience, and were six lines long or shorter.
It was a surprise to find that the restriction on length (imposed by the need to fit on the card) eliminated at a stroke some 99% of poems ever wrtten: even poets with a reputation for brevity would be excluded en masse. Then the poems must be out of copyright, which means, these days, that the poet must have died at least 70 years before (that is, by 1940). In practice this means that almost all the poems are of the short forms of haiku and cinquain.
From within this limited pool, the poems were selected to reflect wisdom, insight, and the elegant statement of feeling, rather than romantic exaggeration, vagueness and complexity that many poets feel they should adopt even when telling the truth.