What are the biggest differences between writing and making music and trying to monetize it as a career?

I am sure there are excelent answers here, in a few words. You can make music easily and its beauty is what you decide to make it. Making money is selling your music or being paid to perform. The second option is much more complex. The busuness side of the experience in my opinion is where the work is and the play starts to degrade. Its been said that the fastest way to ruin a great hobby is start being paid to do it.