Imagine ranking all the shareholders of the company. For each, you've asked them how much you'd have to give them to convince them to sell.

At the top of the list would be the one who is the most interested in selling, and thus is willing to take the lowest price. At the bottom of the list would be the person who is the least interested in selling, and is demanding the highest price.

In order to buy one share you ask the guy at the top of the list. But to get the whole company you need the guy at the bottom of the list to agree too.

That's definitely not a perfect analogy at all, there's more subtlety than that. But it accurately describes the underlying dynamic.

For the stock market quote, you're always talking about the guy at the top of the list.