What's the "I'm feeling lucky Button" on Google homepage?

It's the button that we use to see on the google homepage. The button that's right next to the "google search" button. But what is exactly the use of that button? I think not all of the googlers really know about it. Am i right?

Well, I was reading an article and there was this one little amusing fact about this button.

Google loses around $110 million in annual revenue for this button. why?

Because this button will automatically take you to the first search result. And for that reason, there'd be no ads showing up when you use this button cuz it prevents the ads from showing up. For example :

When you type "download firefox", you will be directed to the page that will give you the download link.

Then why are they still providing the button if they lose so much money cuz of it?

maybe they already make a lot of money, and losing $110 million doesn't really make a difference to them. At least that's what i think. hehe...

Cheers!