Purpose: to detail some of the places where interacting with Tcl leads one to frustration, confusion, aggrevation, anger, hatred, ... (''you get the idea...'')

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[glob]: the need to somehow quote the '''glob {}''' combination so that
one gets the quotes passed on to glob.  Use quotation marks (") or braces around the arguments to get them pass the parser.

[Regular expressions]: a similar problem - the need to quote arguments appropriately so that various regular expression metas make it through the tcl parsing.

Tcl comments: [Why can I not place unmatched braces in Tcl comments]

Tcl hashes vs arrays: Sometimes people attempt to simulate 2 or more dimensions of arrays using the Tcl associated hashes (aka tcl arrays).
The gotcha here is that because the array index is a string, white space
is significant.

 $ set a1(1,2) abc
 abc
 $ puts $a1( 1,2)
 can't read "a1( 1,2)": no such element in array
 while evaluating {puts $a1( 1,2)}

Another gotcha here is trying to set arrays with white space:

 $ set a1( 1,2) abc
 wrong # args: should be "set varName ?newValue?"
 while evaluating {set a1( 1,2) abc}

You need to use quotes if you are putting space into that variable.