In honor of my hematology/oncology rotation, I've started to read (or, better, listen to on audio format) The Emperor of All Maladies by Siddhartha Mukherjee. (A quick testament to how amazing this writer is- when he opens his chapters with quotes from literary giants, I often can't tell when he's done quoting people and has started the text. He's that eloquent.)
Mukherjee describes the early breakthroughs in cancer treatment achieved by Sidney Farber. Farber started with leukemia because it was the easiest cancer to measure accurately- all he had to do was count the white blood cells in a quantity of blood to track the progress of his latest treatment.
After counting, and some trial and error, progress was inevitable.
More importantly, until Farber started reliably counting something about cancer, zero progress had been made for thousands of years, and it was decided that treatments for cancer were impossible.
I can't help but extrapolate to the modern self tracking movement.
Self tracking is ultimately about counting the previously uncounted: sleep, activity, happiness, literally any parameter that one is interested in. The premise is the same as Farber's- once you have reliably quantified something, only then can you make genuine progress towards improving that condition.