Vert this joyful is something I'd also been struggling with a little and already decided it needed a slightly wider interpretation, when someone upthread (sorry, forgery who) posted that the English translation is not exactly joy, but maybe more in the direction of resonance. So taking your toilet paper example i would say if you open the cupboard and find hundreds of toilet rolls - well, unless you've got endless storage you don't need them do you? And they hardly cost the earth to rebuy. So you'd donate all but a month's worth.
If you open the cupboard and find 4 rolls, but jumbled up with all your other stuff, then you'd tidy them away as per the normal method.
And if you did have hundreds and did have room to store them after all the Konmarie-ing then you at least would know you've got hundreds and to stop mindlessly throwing them into the shipping trolley every week.
In the more concrete example of your bras, your boobs will stop going up and down soon and both of mine speed nursing in the day somewhere between 12 and 18 months too. When you're only feeding morning and evening you can ditch the worst of the bras and get some normal soft ones - you can pull down under the boob to nurse. My worst nursing bras got chucked when ds2 was around 12 months, i just couldn't bear the sight of them any more!