Knowing a company's intrinsic value is like knowing a new car's invoice in the sense that, when you know the car's invoice, you know whether you're paying a fair price or paying too much. Is this difficult to understand?
Like you're getting a "fair" price for a stock as long as you don't pay too much more than the seller paid for it.
If you buy AT the invoice price, you still may not have received a good deal. The invoice price may have been higher than the vehicle's intrinsic value.
Let's try this: Suppose you buy a house from its current owner. Should it matter to you what the current owner paid for the house? You apparently would say "yes." But what if the current owner got ripped off -- paid $250,000 for a house with an INTRINSIC VALUE of only $100,000? Then you're "fair" price, which is determined on the basis of the current owner's purchase price, is a rip-off too.