Google Is Personalising Main Search Results

Google uses your search history to personalize your search results. I guess search engine optimization is getting harder. Search results now depend on the user and will be different from user to user.

Read Personalized Search Help:

As a My Search History user, you’ve been storing a history of your searches and the search results you’ve clicked on. Personalized Search now uses that history and orders your search results based on what’s most relevant to you. Early on, you may not notice a huge impact on your search results, but as you build up your search history, your personalized search results will continue to improve.