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Imagine this: In January, you buy a mattress made by a manufacturer called Sleep King. All of the reviews have dubbed this mattress the longest-lasting, softest and most comfortable mattress you can buy today. Your friends beg to come over just to lay on your top-of-the-line, newly released mattress for a minute or two. You sleep with a grin each night. You love your mattress. In February, another company -- we'll call them Snoozy's -- releases a mattress that is softer, more comfortable and longer-lasting than yours. Reviewers rave, and you feel a pang of regret: If you had waited a month, you could be sleeping on that clearly superior Snoozy's mattress instead! No matter, though -- you still have a pretty good mattress from Sleep King. Water under the bridge.