Somewhere in the endless Ethereum space there is a Throne that is waiting for you.
In order to take the throne and to become a Duke, you have to pay - but do not worry, the money will be returned to you, with some additional bonus. Or not.
See, every next Duke of the Ether Throne pays more than a previous one, and the moment the Throne is taken, the previous Duke gets those money. Think of the golden parashute.
Example: a current Duke (you) paid 1 Ether for the throne. Then an usurper came. He paid more (say, 30% more). And that's it: you are not a Duke anymore, and an impostor sits on the throne! Bad news? Not quite...
See, as he paid 1.3 Ether, you get back 30% more than you paid! Also, which is even more important, your name is written in the list of Dukes, and it will stay there for as long as the Ethereum itself exists!
A problem most of the companies face, smart contracts based companies included, is promotion. We want people to know about our little business in order for it to grow. And we are willing to pay for it.
"Share Holder" provides the most straightforward way of doing so. Here is an example.
First, we have attached our "Share Holder" contract to "Duke of Ether" contract (one we want to promote). Now part of the profit "Duke" produces goes to "Share Holder".
"Share Holder" contract sells up to 10,000 shares at a price that can change from a preset minimum and up, depending on the profit the "Duke" contract sends to it. When you buy it, you pay current price, when you sell it, as "Duke" can only put money into "Share Holder", it is guaranteed that you will get more than you paid.
So it looks like someone gives away the profit of a company. For free. However, it is not quite so: a shareholder gets as much profit as an attached contract (in our example it is "Duke", but we plan on adding more contracts) brings. Therefore, we expect a share holder to actively bring new people into our business; in other words, we pay our share holders for an advertizing campaign.