I'm not here talking about their ergonomics (which are rather horrible), but about an infamous flaw in the Joy Cons, which should have never went into production.
The Joy Cons are the two half-controllers that attach to the sides of the Nintendo Switch, and can be detached (allowing them to be used when the Switch is docked, or even when it isn't, especially if using the grip peripheral, or even on their own. Some two-player games even have each player using one of the controllers.)
When used detached, they have strap attachments that ought to be connected to them.
Most people don't notice it, but the left Joy Con has a "-" symbol at its top, which ought to match the equivalent symbol on the strap attachment. Likewise the right one has a "+" symbol.
For an unfathomable reason, however, they can be attached in the wrong orientation (ie. upside down, or on the wrong Joy Con, likewise upside down).
An extremely basic principle of engineering design is that if two parts can be connected, and there's a wrong way to connect them, the parts ought to be designed as to make it impossible to connect them in the wrong way.
A floppy disc is the perfect example of this: Even though there are eight possible orientations for a floppy disc to be inserted into a floppy drive, you can only insert it in one way. In any other orientation it won't go all in (in four wrong orientations the floppy disc is too wide to fit in the slit, and in the remaining three wrong orientations it won't go all the way in because there's a diagonal notch designed to stop it.) Likewise an USB connector cannot be connected upside down because it's designed non-symmetrically, and will simply not fit that way.
It would have been quite easy stopping the strap attachment from being connected to the Joy Cons upside down (by using a non-symmetric design in their rails), but for an unfathomable reason they didn't do that, and it's in fact very easy to do.
Ok, no harm done. Oops, it's the wrong way. Just take it off and connect it correctly?
Except that here's the absolute failure of the design: There's a locking mechanism that keeps the attachment firmly connected to the Joy Con. A locking mechanism that's easy to open when the two parts are connected properly. The problem is that when connected upside down, the locking mechanism will still lock the attachment in place, but now there is no easy way to unlock it. The attachment is very firmly stuck, and there is no easy way to remove it. The unlocking mechanism doesn't work if the attachment is connected upside down.
People have broken their Joy Cons trying to remove a wrongly inserted strap attachment.
It is, in fact, possible to unlock the locking mechanism, but it requires a flat tool, like a thin screwdriver or other such object (you can insert it between the Joy Con and the attachment from the right spot, and it will unlock the locking mechanism, freeing the attachment). However, obviously the vast majority of people don't know this.
It's astonishing how this kind of design flaw went unnoticed and into production. It's one of the most basic things in engineering design.