I’ve always thought that this is supposedly the correct ‘slip knot’ and the one I usually do which is tying a knot with one hole on it before putting the string in there is not actually the real ‘slip knot’.
But what do I know…
I feel like this kind of knot is only useful if you plan to do string break trick on stage, otherwise you’re effectively halving the strength of the string near your finger by threading into the string itself instead of going around it, there is a lot of pressure in there.