Finding out that you have made a mistake on something can be a pretty big deal depending on what you are talking about.  Luckily, when you are talking about seo there are always ways to go back and fix what you have done wrong.  However, it will take some time and also learning how not to make those seo mistakes again.  The time that you will spend fixing your errors will more than make up their value in money.  I have learned  a lot from the Internet over the years.  Whether I paid some money for the knowledge or got it free.