Tried to search around the forums, but couldn't find an answer to this.
Do you think that your current phlegm levels affect the success rate of planing wood? Besides Hammer & Nail level of course. I tested out with 89 phlegm and 81 Hammer and Nail. When my phlegm was half-filled, I destroyed nearly an entire backpack of planks. When it's mostly filled, success rate is about 2/3. Mere coincidence? I think today was the second time it happened, I was pretty surprised when I started destroying most of my planes until I decided to refill my humours.
I read somewhere that phlegm levels affect the usage of a tinder drill. Maybe it does play a part in other actions as well?