You are very right. When I worked as a content writer I did a huge volume in one week and realized that 10,000 words a day isn't sustainable for any length of time. The flip side of this is that I feel bad if I don't do my 1,500 words. Luckily I'm at a place where I can pick and choose my projects and only take the ones that pay the best. Having a partner that brings in a regular income is a huge help.