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It is interesting but very counter-intuitive. The basic idea is that in an ordinary single-price sealed-bid auction, there is a strong tendency for bidders to cut back on what they bid, figuring they only have to bid higher than the next highest bidder. In a Vickrey auction, named for the guy who thought of it about 60 years ago, the winning bidder is still the one who offers the highest bid, but what the person pays is the value of the second highest bid.

For reasons given in the link, there is an incentive for bidders in a Vickrey auction to bid what they are willing to pay. The question then is whether the second highest bid, which is what is paid, is higher than the highest bid in an ordinary sealed-bid auction. It is not clear to me why that should necessarily be the case.

One thing of interest is that a sealed second-price auction resembles an open, multi-bid auction. When people can change their bids, the winner will be the person who bids more than what the second highest bidder is willing to offer.