What affects the stocks price?

Hi,
   I believe if you have purchase a stocks before, you will know that the price of each stocks differs every day. Sometimes, you purchase at a price which is perceived to be high, while at other times you may purchase it at a low price. So what makes a stocks price moves up and down?

It all boils down to a few factors:

1. Economic news and events of a country
2. Company earning announcement
3. Forecast earnings outlook
4. Analyst upgrades and downgrades
5. Mergers and Acquisitions
6. Confidence to Management level
7. Lawsuits
8. New product launches or failures
9. Insider buying/Selling

With all this few factors in mind, you need to be nimble to closely monitor your stocks such that it will not become a worthless piece of scrip.