I've just lost a small part of my audio collection, by a stupid mistake I made. :-( 
GLADLY I had a fairly recent backup, but it was still irritating. Apart from yours truly, the other culprit doing the mischief was `mv`, which will show as follows: 

The audio files had a certain scheme: 

 ARTIST - Some Title YY.mp3

where `YY` is the 2-digit year specification.

 mkdir 90<invisible control character>

(Up to this moment, I did not know that I had actually typed one third excess character which was invisible ...!) 
Instead of having all in one directory, I wanted to have all 1990s music in one directory. So I typed:

 find . -name '* 9?.mp3' -exec mv {} 90 \;

Not so hard to get the idea what happened eh? :-> 
The (disastrous) result was a virgin __empty__ directory called '90 *something*' (with *something* being the "invisible" control character) and __one single file__ called '90', overwritten *n* times.

ALL FILES WERE GONE. :-(( (obviously)

But this would not have happened if `mv` had __checked__ in time whether the signature of the destination "file" (remember on *NIX everything is a "file") starts with a `d------` (e. g. `drwxr-xr-x`). And, of course, whether the destination __exists__ at all. Because there is also a variant of the aforementioned scenario, when you simply *forgot* to `mkdir` the directory first. (but of course, you assumed that it's there...)

Believe it or not, your pet-hate OS starting with the capital __W__ DOES DO THIS. You get even *prompted* to specify the type of destination (file? directory?) if you ask for it.

Hence, I just cannot believe that we *NIXers still have to write ourselves a "`mv` scriptlet" just to avoid these kinds of surprises.