When it comes to investing, my suggestion is to first understand your strengths and weaknesses, and then devise a simple strategy so that you can sleep at night!
Ben's emphasis was on protecting his expectation of profit with minimum risk.
We don't put the same amount of money in each stock.
Be aware of the level of the stock market. Are yields low and PE ratios high?
Use book value as a starting point to try and establish the value of the enterprise.
We get a feeling, if we can, about what we think the company is worth.