I don’t remember all of the details, but I thought it was essentially the water’s surface tension that foots the energy bill when climbing a paper towel or a capillary in a tree.
The surface of fluids like water are unhappy. Molecules on the surface would much rather be deep in the fluid because on the surface they have “dangling” Van der Waals & polar bonds to one side. You can calculate the potential energy of the surface due to all of those dangling weak bonds, & that’s the energy that is used to climb a capillary (the energy isn’t free).
I could be misremembering though, I admit. School was many years ago…
I recently learned to whistle as well! (in my late 30s). I’m bad at it, but finally can make a recognizable tune.
More recently though I’ve learned to cut my own hair :)