Goldilocks state where one is neither too impressed nor unimpressed, but gives the 'just right' response? As irony would have it, the archaic English word 'whelm', from the Middle English 'whelmen' meaning 'to capsize' or 'turn over', means overwhelm. So, to be whelmed itself means to be overwhelmed.
But, over time, people not happy enough to showcase their enthusiasm or appreciation for something merely being 'whelmed', added an 'over' — a prime example of our hyperbolic culture. So, between the value of showing being over-, under- and 'plain' whelmed, being underwhelmed must be recognised as an aristocratic gesture, one the mob will find strange, and, in due time, view with awe when the Age of OTT subsides.
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