Peter Cundill on the timing difficulty of selling

From There's Always Something to Do:

As I proceed with this specialization into buying cheap securities I have reached two conclusions. Firstly, very few people really do their homework properly, so now I always check for myself. Secondly, if you have confidence in your own work, you have to take the initiative without waiting around for someone else to take the first plunge. I haven’t yet found a solution for determining timing on the sell tack. People say it ought to be largely dependent on one’s perception of the trend in the overall stock market, but I am suspicious of this. I think that the financial community devotes far too much time and mental resource to its constant efforts to predict the economic future and consequent stock market behaviour using a disparate, and almost certainly incomplete, set of statistical variables. It makes me wonder what might be accomplished if all this time, energy, and money were to be applied to endeavours with a better chance of proving reliable and practically useful. The timing difficulty in selling does not lie in not knowing when the trading discount to intrinsic value has been eliminated, but in judging by how much it is likely to be surpassed.