I recently found myself saying that this expression was among the most powerful of sentiments. I have stopped making any distinction between the language used to express a sentiment and the sentiment itself; the two are so closely related that one begets the other. To put it bluntly:
If I feel "never mind" I say it so:
And if I say "never mind" I don't mind.
It is supposed that, "never" originates as an emphatic form of "not" (ref.) which makes the expressions amazingly ancient and unchanged - "mind" as a verb being to think about, keep thinking about or "hold a thought". Expressions which endure unchanged generally do so because they come not merely to encapsulate linguistically the intended meaning, but to represent it so symbolically that there is little functional difference between the sentiment and the use of the phrase to express the sentiment. To put that one bluntly:
Saying "never mind" is the same as not minding.