The reason your knot does not come undone has nothing to do with tension and everything to do with the order of the way you tie it. Left over right, then right over left. If you learned the standard knot as a kid in the right order and continue to do it the same way today, then the Ian knot will tie the exact same knot. The only difference is that the Ian knot will wear your laces more evenly and it ties faster.

Knots I've tied Ian's way are the most taut, precisely because I have no issue applying tension all the way, instead of the old method with switching hands and stuff, where that was impossible.

If you're doing it right, the result is not like keeping a finger on the slipknot - it's better (and simpler, faster and as taut as you want).

I didn’t mean that tension keeps my knots tied (though clearly some tension is necessary), it was two separate replies — and I’m pretty sure I make granny knots. Eh maybe knot.