Full Disclosure: I write this on the morning of our office holiday party. The afternoon is a write-off, and from here until the New Year Executive Platforms will probably never have a working day where all hands are on deck again. From now on, everything will be done with an understanding that things may take a little more time or even need to be put away for a while. Businesses everywhere are entering a period where productivity is going to fall off, and there is nothing even the best manager can do to prevent it. In fact, the best managers…