Quote from Laissez Faire:
Please don't short this market today. The only signal I can see right now would be, "the market is too high", but that is not a signal.
If shorting, at least average up as Livermore used to do. He would only add to his position if the market proved him right, not the other way around.
He once averaged down so massively that he liquidated a winning position to be able to meet his margin call and continue averaging down on his losing position. That lesson and the major loss that eventually followed made sure he never averaged down again.
One huge loss is all it takes.