About 9 years ago I had a run-in with stomach cancer. After a few months of chemo and a 7 hour operation I was eventually declared cancer free and have been ever since, but still have to live with the consequences of the treatment and be vigilant for any signs of it returning.

I still suffer intermittent stomach aches, especially in the early hours of the morning, and had a terrible time trying to decide if they were getting better or worse over time.

Our narrative voice is awful at detecting long term trends and tends to overcompensate for particularly good or bad patches so it was impossible for me to judge and I started keeping records of how bad the aches were each day.

Long story short, the average severity was mostly decreasing over time and the average time between bad aches was slowly increasing but it would have been impossible to tell if this was happening without keeping detailed records because it wasn't consistent - some months were much worse than others and completely skewed my perception of long term trends.

While most people hopefully won't ever need to do something like this, it did make me realise just how bad we are at picking up on long term trends so I can definitely see keeping daily records of, for instance, average daily happiness being eye-opening.