Hmm I think your 'friend' is probably not very experienced with online earning or he was deliberately misleading you. I actually feel like most people have said, you are best off diversifying your income streams to avoid leaning too heavily on one source. It's still ok to have a 'strong point' like what you're qualified in, but you can also look into something else to add to your list of earners. For instance, I have a clutch of beer money earners, my freelance site as well as my remote online teaching. I also do remote translation and editing work.