Why do businessmen attach a great deal of importance to letter writing?

Letters (memo's and other similar documents) often form the paper trail of a projects. They reveal what decisions were made, why they were made and the expectations of both parties in the deal, arrangement or contract. If a project goes south the legal settling of the blame may rest on the clarity of the letters provided.

Lets make up a case of a poorly written letter. Assume you are in receipt of a letter from your boss. Your job is to water his office plants. The instructions in the letter say: Remember, the plants cannot be watered too much.

Do you interpret the note as meaning "Only water the plants when they need it" or as "Drown them, they'll love being under water."

A clearly written letter would have said: Water the plants with a half liter of water per plant each Thursday (December 12 and December 17)