How long to stay invested in a stock?

Yesterday night, I was speaking with a very respected friend, elder and we discussed about investments & businesses. We started talking about strategy and then he revealed that he was invested in two stocks. I definitely endorsed his strategy, since I, myself am invested in a single business and am enjoying the benefits of that greatly. We started talking about his picks and then I realized that both of his stocks were pretty richly valued in terms of PE. I, then suggested, him to move to a stock which was equally good & of high quality but quoting at undervalued prices. Later, I realized that this was worth writing an article.

What is an ideal business?

What's a business meant to be? Surely, its not for emotional gratification. Its meant to earn you money more than what you invested in raising the business over a period. You expect returns. 

You can't alone run a business. You need co-operative efforts of employees for which they get paid. So, employees are a great asset for the business, but not at the cost of returns from the business. So, definitely, business isn't welfare. Any incompetency & any expensive labour needs to be sorted out.

Business is also run by machines and machines need buildings and buildings are erected upon lands. These all comprise "fixed assets". Their expense come up firsthand while initiating an enterprise. The amount paid for the "fixed assets" must be conducive enough for the profitability of the business. Lets us take the example of land. If the land cost is so prohibitive, then it can affect the expansion of the business which relies upon setting up manufacturing units for itself. Second is the case of machines/technology.