I think the point being made is about having a model, to be able to exit in time, before the market goes to crazy valuations.
We have had peaks/mania followed by big crash in 1984, 1992 (Harshad Mehta scam I was witness to), 2000 (dot-com mania) and the 2008 (crash that all of us must have witnessed). Bull Market peaks have followed roughly a 8 year cycle in India (now don't kill me for that generalisation). So there is one round the corner, more likely than not.
The way markets are behaving today, all kind of stocks going up (with reason and without reason too). All signs are leading to a stage of crazy valuations, sooner than later, who knows maybe by 2016. or within 2 years.We seem to be able to rationalise that stocks like Astral will continue to deserve the 50x trailing valuations - that this will continue - should even get better!! no black swan event will be forthcoming, this time it is different
But most folks seem to be unwilling to rationalise that Astral like stocks which are already seeing very rich valuations can also Reverse to the Mean - within 2-3 years or a P/E of 25-30. Everyone seems to think this is perpetual, and for keeps.
Time to get real. And be prepared to swing depending on how it goes. If valuations don't go to extreme levels - great, don't sell even marginally, that's your call.
But if it starts/does go to extreme levels, there's not much of a rational argument left about not progressively booking profits.