Number line: Ok, the 0 is like the flipping point but, big deal, you can also spin the number line around and make the positives into negatives, and the negatives into positives. You just have stick the whole thing on a pin with the zero in the middle, spin it until it faces the other way and boom – -1 becomes +1, -1000 becomes 1000 etc.
Trifoil is different. There’s no point of balance like that… you can’t spin it around to make it into its opposite because the opposite is always different.
If you want to turn your left hand into your right hand, you’d have to turn one of your hands inside out.
But then the inside of the skin would be on the outside, and the outside of the skin on the inside, so even in that case, one didn’t become the other.