I have also tried idea of buying business with PB * PE close to 22.5 as per Graham formula, but with some success. Tata Chemicals, Ambika are those success examples. Some others have not worked. Off course I also look at business quality, ROE/ROCE and management quality.
The slide on Selling is also interesting. I am also holding Sonata for high dividend yield story, moderate growth and low PE. So far still holding with patience but things are not moving as envisaged. This is the difficult period for me, when I have to keep holding positions as I believe in holding period of 3 years and above unless stock gets overvalued.
Art of selling is indeed difficult to master. @desaidhwanil has done a very good presentation on selling decisions and it is here ->
In a nutshell, following things make sense for selling ->
When initial investment thesis has changed or no longer valid or incorrect. e.g. If you bought a story as undervalued bet and valuation has caught up, it might be good time to sell. If your business thesis (growth, margin expansion, dividend etc.) is not working out (irrespective of stock price) for decent amount of time period it is time to sell.
If you have found a better story where risk adjusted expected return is much higher than one of the existing stories, it might be time to sell.
For an investment that started in your portfolio as AB (attractive business), it might be time to sell if competitive position has deteriorated or business quality is going down (declining return ratios, more capital requirement, management mis-actions etc) or balance sheet has worsened (debt, equity dilution etc.) or if you think industry as an whole is going through bad phase for long periods (3 years+).
Another thing I tend to do is sell AS (Attractive Securities) when overall market is in very bullish territory even if my targets are not fully achieved e.g. when Nifty, BSE small/mid cap index PEs are around (long term average + 3*standard deviation) (PE of 25+), I tend to sell my AS.
This is where many of us may not get it right.
We may continue holding over valued stocks if we believe in the story or they are reasonable valued. Based on NIFTY PE some of us may not sell individuals stocks, and if market corrects, then we may not have cash to invest heavily.