To answer this you need to know the most important principle of Stock investing: The fair value of a stock depends on its ability to generate profits consistently, and that the market prices in the long term always depend on this.
Therefore it is sensible to anchor the buying price to a stock’s fair value. You may buy at a discount to its fair price to be on the safer side or close to the fair price.
However, this is not a simple straight-line affair because of what happens every day in the stock market.