On my system, man -2 stat enumerates

EACCES

Search permission is denied for one of the directories in the path prefix of path. (See also path_resolution(2).)

EBADF

filedes is bad.

EFAULT

Bad address.

ELOOP

Too many symbolic links encountered while traversing the path.

ENAMETOOLONG

File name too long.

ENOENT

A component of the path path does not exist, or the path is an empty string.

ENOMEM

Out of memory (i.e. kernel memory).

ENOTDIR

A component of the path is not a directory.

And I don't see anything there for read failures (incl communication failures with remote volumes).

perl -MErrno=ENOENT -le'
   $found = -e shift;
   die("stat: $!\n") if !defined($found) && $! != ENOENT;
   print($found ? "found" : "not found");
' file
[download]

One I thought would trip it up is doing a chmod 000 on a file owned by root and testing it existed using a non-root user. Nope, you still get the -e returning true. (Which does seem to be the desired semantics, since the file does exist.

Update: Ahh, here's a case. If the user running the script cannot cd into the directory containing the file, then -e fails.

Do chmod 000 on the directory containing the file and it won't be found for non-root users.

$ perl -MErrno=ENOENT -le'
   $found = -e shift;
   die("stat: $!\n") if !defined($found) && $! != ENOENT;
   print($found ? "found" : "not found");
' foo/bar
not found

$ touch foo/bar

$ perl -MErrno=ENOENT -le'
   $found = -e shift;
   die("stat: $!\n") if !defined($found) && $! != ENOENT;
   print($found ? "found" : "not found");
' foo/bar
found

$ chmod a-x foo

$ perl -MErrno=ENOENT -le'
   $found = -e shift;
   die("stat: $!\n") if !defined($found) && $! != ENOENT;
   print($found ? "found" : "not found");
' foo/bar
stat: Permission denied
[download]

Most often the simple fact that the path is not what you think it is. Maybe the variable doesn't contain what you are SURE it must. Maybe it contains a little more than you think. A space at the end, a newline maybe. Maybe you forgot to double your backslashes (if you're using Windows). Maybe the current directory is not what you expected. If a -e $variable returns false while you think it should return true print "\$variable=>$variable<\ncwd=>" . getcwg() . "<\n";