There was once an accounting firm where the senior CPA knew everything there was to know about accounting. He could answer any question. He knew all the tax laws. There wasn't a better accountant anywhere.
Every morning when he came to work, he would unlock his desk drawer, open it up and look inside for a moment, and then close and lock it again. This puzzled all of his co-workers, because it was the only eccentricity that this genius exhibited. For years no one dared to breach etiquette and snoop through his desk, but his odd behavior became something of a legend around the office.
One day when the elderly man was home sick, one junior accountant could control himself no longer. Taking a letter opener he carefully pried open the desk lock. Inside he found one sheet of paper, and written in large letters was:
"DEBITS ON THE LEFT...CREDITS ON THE RIGHT"