I have heard that an SOP for a PhD should be 60% future (what you want to do) and 40% past (what you've done). We all want to talk about how great or inspiring our lives were to lead us up to this point, but you want to get INTO the program so you can keep moving forward.
Personally, I think you should lightly touch on the fact that you found out 9-to-5 work wasn't for you - tie it all back to the fact you want to continue the learning process, be intellectually stimulated by admittance into the PhD program, and be innovative with your ideas in the field, given proper training and support. Make it clear that your interpretation of higher education is not "drudgery," but creativity, progress, and optimism.
Granted, I am still working on mine as well, but I definitely have not written the bulk of it in one fell swoop. I've had the document on my computer for a few months now, only pulling it up when I feel especially motivated or if I happened to remember an awesome phrase / concept that I could work in there. Lucky that we have digital word processors that you can type whatever and drag it around afterwards. Maybe it would help to not write it beginning to end; just start typing, really get into the meat and potatoes of your interests, and you can edit it to your liking after.
Good luck!