And some idioms might make sense, but they're used in a way which deprives them of sense.
For example: "Well, that's the exception that proves the rule!"
There are a number of ways to make that make sense, such as the use of "prove" to mean "test", as in "proving grounds", so that's the exception which tests the rule, or, alternatively, the fact it is an exception is proof the rule exists in the first place. Both sensical interpretations.
Of course, it isn't used like that. It's used more like this:
A: "Women can't program!"
B: "Wrong. Look at Grace Hopper, to begin with."
A: "Well, that's the exception that proves the rule! Women can't program."
For example: "Well, that's the exception that proves the rule!"
There are a number of ways to make that make sense, such as the use of "prove" to mean "test", as in "proving grounds", so that's the exception which tests the rule, or, alternatively, the fact it is an exception is proof the rule exists in the first place. Both sensical interpretations.
Of course, it isn't used like that. It's used more like this:
A: "Women can't program!"
B: "Wrong. Look at Grace Hopper, to begin with."
A: "Well, that's the exception that proves the rule! Women can't program."
B: facepalm