The self-trimming wick is the trick. Before that was invented, people had to use special scissors to trim the wick and avoid uncontrollable large (and flickering) candle flames.
https://en.wikipedia.org/wiki/History_of_candle_making#Indus...
https://en.wikipedia.org/wiki/History_of_candle_making#Indus...
Weirdly, the trick wasn't in changing the wick material to burn better, but changing their shape so they curled over (and remained marginally in the flame until burnt) instead of just sticking straight out: rectangular instead of circular braided string.