Most people think that making money is very easy.  Just type anything and you get money through the ads.

Yes it is true ....... but the question is how much money do you want to earn? Just 0.01 cents? or 100$ or .......

I made a mistake of running a website for 5 long years hoping to earn a lot......

http://hubpages.com/hub/Money-making-mistake-I-made-for-5-long-years

but only after 5 years I realized that it is just not about running a website, but what the website is about... how much demand is there for the article..... how much are advertisers willing to pay for the ads....

If you write an article there are words in it called keywords.... it is these keywords which determine how much you get paid....

For example if you write an article about Things to do in Antarctica, there may be hardly a few people searching about it and so few advertisers if at all.  However, things like insurance are searched by a lot of people and so more advertisers come into the picture creating more competition and willing to pay more and you get more money from the advertising out of it.

So all you need to do is find out topics that are in great demand and something which everyone needs so you will have more readers and more advertisement and more money....