For myself, I happen to be a professional in a realm where most participants are amateurs – Free and Open Source Software. (Whether most of the core code in FLOSS projects is written by amateurs or professionals is subject to a lot of debate, but I think it’s fair to say that counting heads rather than LOC results in more amateurs than professionals.)

For my part, the transition from amateur to professional was one of luck and the law of averages. I spent a ton of time on my FLOSS projects while working as a professional developer; eventually one of my bets was going to hit. Maybe the biggest factor is having the courage (or the foolishness, or the desperation) to take opportunities to professionalize your hobbies when they come up.

On a last note, I think that it’s a myth that professionalisation inevitably leads to a loss of integrity and unethical behaviour. That’s a personal choice; nobody can make you do the wrong thing for money, and there’s always a good business providing high-quality products or services to consumers or an audience in an ethical manner. Money is not the root of all evil; it’s just a convenient excuse for people who don’t want to take responsibility for their choices.