That’s a big “if”. I really don’t.
This is how I pack for trips: A shirt, pair of socks and a pair of underwear are folded/rolled together. Bras are kept separate. No searching to find the socks which match the shirt. I don’t include shorts or trousers, because those will change depending on the temperature. I don’t do this at home, as I have many more permutations, as I have more pairs of shoes, hence more sock choices.
Hubby has multiples stacks of tshirts. He has a method to ensure FIFO. Which is why he folds his shirts and puts them away.
Resist tyranny!!! 
I can see that that would work well for some people. I rarely wear shoes at home, though, so I put on a fresh pair of socks every time I wear shoes when I go out. Which could be anywhere from zero to two or three times in a day. I’m just not going to re-use a smelly pair of socks, even if I only wore them for an hour or two. It’s not like extra pairs of socks won’t fit in the next laundry load. OTOH, the number of pairs of underpants I wear in a day is almost always 1.
I’m the reverse. I usually use one pair of socks a day, unless I’m dancing hard, when i might use 2 or even 3. But I’ll never put on a used pair of underwear, even if I’ve only with it for an hour. So if i take a shower mid day, I’ll always change my underwear.
Statistically, I can’t see how FIFO makes your underpants last longer as a whole. In fact, if you wear all your undies at equal frequency, that means they’ll all get worn out at the roughly the same time, which can lead to a crisis.
You don’t turn them inside out for a second wearing? 
I don’t find this to be true. They will all start wearing out around the same time but not exactly the same week, so first one pair goes into the trash, then a couple of weeks later another one gets tossed. Now I’m on notice to go buy a couple of new packs.
But before you buy them, if you suddenly need a pristine pair of underpants for a special occasion, you don’t have one, whereas I have a whole bunch of them at the bottom of my pile.
I was taught one should always wear clean underwear in case one has an accident; but isn’t that what an accident is??? 
Seriously, who sees my underwear except my SO, the doctor (scheduled physical) or someone glancing over in a locker room? If I’m wearing a tux at a wedding no one there should see my underwear short of a split pants wardrobe malfunction. What kind of special occasion do you need pristine underwear for?
Well, to be blunt… if you think there’s a chance you might be gettin’ some, so to speak, then wearing nice underwear is only polite (and may increase your chances!)
Says the guy with underpants on the outside
Yes, this is the only situation where i think it might matter. My doctor never sees my underwear. They talk to me for a bit, then ask me to uncover whatever parts they need to physically examine, and leave the room while i do that. I usually shove my disreputable underpants into my pants when i disrobe.
I suppose the ED doctors or the EMS team might see my underwear while cutting off my clothing after a major accident, but i can’t imagine my somewhat worn-out underwear is remarkable enough that it would distract them.
But i like to have a range of underwear because:
1)
possibly tmi
When i have a rash, a really plush, new pair may be better for my crotch
i like to go through the pretty-good underwear, leaving the maybe-should-replace-soon pairs, because if I’m lazy or busy and don’t want to do laundry, it gives me a week’s leeway of “I’d be happier if i did a load of laundry, but this is good enough.”
So I’m very happy putting the freshly-washed on the top of the pile, and digging through the pile to find an appropriate pair for today’s needs.
I’m in a long-term, monogamous relationship; she’s more concerned with what’s in the underwear than the last garment to be removed, sometimes in conjunction with another garment or sometimes under the covers & out of view anyway.
Do not dare confuse me with Messrs Wayne or Kent. 
Same about not putting used underwear back on, but since I rarely have a need to take showers midday, I rarely need a second pair of underwear.