For me, it was the difference between assumptions/inferences and repeatable measurements... Being typically human, I was able to be unobservant, post-rationaliz

For me, it was the difference between assumptions/inferences and repeatable measurements... Being typically human, I was able to be unobservant, post-rationalize my poor sleep, believe I still had the drinking constitution of a 20-year-old, and otherwise ignore the effects. Having months of daily Fitbit records that I could look back on well after I forgot about my "rough morning" the following day drove the point home as only hard data could.