Not to take a position in this debate as a whole, but I just want to interject that there is research suggesting that you actually are more likely to be affected if you are aware of the other person's conflict of interest. (Can't find a link right now...)
If memory serves me right, the theory is that it makes you overestimate your ability to stay objective and unaffected, so you're effectively lowering your guard, or something along those lines.
The point I was making by comparing to a pilot, which I realise I could have expressed a lot more clearly, is that it is perfectly possible to mitigate risks through proper training and procedures even if it's not possible technically. (I.e. all it takes for a plane to crash is to turn the flight controls a few centimetres in the wrong way at the wrong time, yet it almost never happens.)
Of course things fail and people screw up. What I don't agree with are arguments along the lines of this just being a slight oversight, and that those can easily happen. It should require serious failure on multiple levels for anything like this to happen at that scale, if they are implementing things properly, not minor oversight.
So here is the thing: It was presumably relatively easy for you to come up with that scenario, which you called "not-unlikely". Then what you do is you put that scenario into your risk analysis when you're designing the authentication architecture, and figure out mitigations to make sure that particular mistake becomes (very) unlikely.
The notion that "it could easily happen" that is being brought up throughout this thread should really only suggests that people aren't doing even rudimentary security assessments (or, hopefully, they're not working with security sensitive software).
If you can't solve it technically, you solve it through processes and training. Same goes for any other industry -- if a construction worker said that it's just one bad morning away from dropping a two tonne girder on a playground, we would never accept that. Or a pilot crashing an airliner into the waiting hall when they're supposed to land. Somehow it seems that large parts of the software industry simply hasn't reached the level of maturity we expect from pretty much all other industries.
Facebook is an enormous company. They should be able to have entire departments working on these topics. It's not a one-person hobby project we're talking about.
It's not tethered to the ground. It's a group of rotating "wings" tethered to each other in the centre, wherein the centrifugal force of the rotation give structural stability. That way they get away with using less structural material, which means more of the weight can be batteries or fuel.
You're right that the feet deform significantly when you stand on them. For that reason you usually measure them load-bearing (i.e. you stand up with even weight distribution on your feet).
I think it's more likely that it's the deformation of the shoe that is uneven than that the shoe affects the deformation of the foot much. An exception would be if it has a built-up sole with support for the arches, preventing the arches from collapsing.
Either way, it's a complex process that is hard to model, just like you say. The way we're getting around it is by collecting various data on what people end up liking and then infer the properties of the shoe, rather than trying to explicitly model it. So the solution is a combination of 3D scanning and machine learning.
Also worth mentioning, by the way: most people actually have slightly different size and shape on their left vs. right foot. For about 50% of the population the length differs by more than half a US size. Being perfectly symmetrical is the rare case.
That method is actually used by many shoemakers when you order a pair of bespoke shoes (in combination with a series of tape measurements). It's not accurate enough to produce a fitting shoe in a single attempt, however, so what usually happens is they make a "test shoe" based the measurements and drawing, then modify the last after having you try that on. This procedure can be repeated more than once if needed.
Knitted socks are quite a lot more forgiving than leather shoes, fortunately, since the material accommodates by stretching when you put it on. I'm not surprised it worked well for you and your aunt!
Perhaps most obviously, you just can't try a shoe on if you buy online. You can if you buy five pairs and return four, as some do, but it's a lot of hassle and a waste of resources for all the shipping back and forth.
Secondly, a significant portion of the population (tens of precent) have "problems" enough that most shoes in a store don't fit, meaning you have to try on a lot before you find one that does. And even if you don't have such issues, sizing between brands (and even styles) is so inconsistent that you usually have to try multiple different sizes to decide which one fits you. Having a 3D model paired with an AI system that tells you which shoes fit and what sizes to pick saves a lot of time for a lot of people, both shoppers and staff.
Finally, if you ever want to order custom made footwear, there is really no way around measuring your feet. And arguably the only reliably well-defined and repeatable way of doing that is to do a 3D scan to capture the shape.
Not only are there technologies that could be used for this, there are working products in the market that do it already. I work for one of the technology providers in this area.
Having x-ray images or such would actually be somewhat helpful, as you could much more easily identify the metatarsophalangeal joints (the joint where the toe meets the foot), the locations of which do influence shoe fit to some extent.
However, the cost, safety, usability etc. of using x-ray machines in a retail setting makes it infeasible by a wide margin compared to optical measurement methods, and those generally take you far enough anyway. I'd rather go for dynamic analysis (i.e. scanning the foot while it is in motion taking a step) if more data on the skeletal structure is required.
Several well-known brands are working on this in various ways. Adidas has a cooperation with Carbon 3D to produce individualised soles for shoes you order, as one example[1]. Robotic knitting is another area I know some players are working on, for making custom uppers. You'll likely see offerings for customised footwear based on these technologies appear on the market in the next couple of years.
I'd expect it to take a number of years before the manufacturing processes have matured and evolved enough to get the price points down to the level that most people would consider an option when buying footwear, though.
Technologies for mass scale customisation is being developed by several big players in the market. However, also consider that there are already hundreds of thousands of different shoe styles in the market, so finding a pair of perfectly fitting shoes can to a large degree be considered a search problem rather than a customisation problem. With appropriate 3D scanning technology, this can be done today.
Disclosure: I work for a technology provider in this field.
> No one uses SMS because it's primitive and limited compared to regular messengers.
You also have to take into account that SMS is 5-10 times more expensive almost everywhere outside the US. Unless you have a flat-rate plan, a single 140 character messages is about 10 cents where I live. And even if you have a flat-rate plan for domestic messages, it's 1-2 USD (per message!) when sent to friends and family abroad. I don't use SMS because it's just being ridiculously over-priced. I want my device to use data to send data, regardless of what kind it is.
If memory serves me right, the theory is that it makes you overestimate your ability to stay objective and unaffected, so you're effectively lowering your guard, or something along those lines.