Sell

Although it sounds depressing to realize nothing is really eternal, the situation is more palatable for the worldly people who do investment.

The logic is simple: Although it is widely publicized that value investors like Benjamin Graham and Warren Buffett buy and hold, and they enjoyed an exceptional investment return, the strategy could hardly be regarded as ideal.

(In reality, Warren Buffett does sell things, and it all depends on the price - see what he did with PetroChina.)

Then, what is the difference between a speculator and a value investor?

The probable answer is this:

• Speculators sell a stock when they achieve a small and pre-defined amount of profit (say, 10% or 20%), or, in response to a fluctuation in the price of a stock, to cut his loss (止蝕).
• Old-school value investors (like Benjamin Graham) sell when the price of a stock rises from a grossly undervalued position (i.e. where they buy the issue) to a reasonable or slightly over-valued one. In general, a day-to-day fluctuation of share price does not trigger him to cut loss, but a fundamental change in the financial condition of a company would - because the valuation changes.
• Modern value investors (like Warren Buffett) sell only when the story of a company (or, actually, the story of the future of that company) does not hold - they won't even sell when the price of a stock (of a good company) is slightly over-valued.

If my description of the two types of value investor is not clear, let's put it this way: The old-school ones buy a so-so company at an excellent price, with an aim to sell it when the price rises to a reasonable level; the modern ones buy an outstanding company at a reasonable price, and keep it as long as the prospect remains rosy.