If you are a normal person, sometimes you change your mind, especially when it comes to your future. I was set on being a journalist when I graduated from high school. It wasn't until the second semester of sophomore year that I learned it wasn't what I wanted to do anymore. I changed my major to speech pathology/audiology and I'm SO glad I did. There are definitely advantages and disadvantages to changing your major, though.
1. Advantage: You finally figure out what you want to do with your life and you're excited to finally get in those classes.
2. Disadvantage: You wasted time and effort in classes that didn't even matter.
3. Advantage: You want to do well in all those new classes because you actually enjoy what you're studying now.
4. Disadvantage: You have to do well in those classes because you don't have time to do poorly.
5. Advantage: You can still (more than likely) graduate on time.
6. Disadvantage: You will definitely be in school year round and you will be overwhelmingly stressed all the time. :')
Even though there are a multitude of disadvantages to changing your major, finding your life's passion is what is most important, and ultimately that is all that matters.
