I still get clients who worry about making a mistake or doing something "not right" when they put a room together. They feel they have to follow an all modern, all classic or traditional style in order to make a room work.
The main reason I think mixing styles makes for the best way to design our home, is because it tells a more layered and true story. We're not one note. We're complex. We are silly and serious, thoughtful and carefree...let colorful kid's art live next to somber "important" photography. Frame them both with the same care.
Plus, mixing styles allows for each to be highlighted in a way that it can't when it's drowning in a sea of sameness.
I will also stick by the motto, "If You Love it, Then it's Right!" Always.