title text: "Friction-driven static electrification is familiar and fundamental in daily life, industry, and technology, but its basics have long been unknown and have continually perplexed scientists from ancient Greece to the high-tech era. [...] To date, no single theory can satisfactorily explain this mysterious but fundamental phenomenon." --Eui-Cheol Shin et. al. (2022)

(https://xkcd.com/2682)
(https://www.explainxkcd.com/wiki/index.php/2682)

LB: SO THIS IS HOW I FOUND OUT WE JUST DON'T KNOW EXACTLY WHY STATIC CHARGE BUILDS UP IN OUR HAIR WHEN WE RUB A BALLOON ON IT WHAT THE ACTUAL FUCK

@Nine IIRC we also don't know that well e.g. why unrolling scotch tape emits light, why steam bubbles emit light when imploding, how exactly does the mechanism behind thermoluminescent dosimetry works (we have some models that very obviously can't be correct for some setups). I expect that there's lots of similar things in solid state physics.

In general my impression was that these things are present the most in cases where the whole setup has a complicated description at the level that's relevant to any reasonable explanation. I expect that you can find a similar set of weird intermediate-level very hard things in e.g. biology, too. Also in math: there's lots of number theory conjectures (e.g. Collatz conjecture) that seem very simple at a first glance.

@robryk .... Wait... What was that about scotch tape?! It does what?!