1.    Google changes their search algorithm about every 3 months.  There are countless sites that had an SEO strategy, were doing well in search, and saw their search traffic plummet after the Google update.
2.    Over 60% of the world’s search goes through Google.com.  Playing by their rules is key to succeeding online.
3.    Google’s algorithm for search (how they determine a site’s ranking order in search queries) is probably one of the most valuable trade secrets on Earth.  They put different weight on different factors.  There is no way to know exactly how these factors work together.  To know them absolutely would be to dominate the Internet for any niche.
4.    Links from .gov and .edu sites are GOLD.  Google gives a huge advantage to these links since they see .edu and .gov sites as having a higher integrity with regards to whom they link to.