Of course I know the Electoral College decides who becomes President, it was designed to reflect the popular vote in times when casting ballots was difficult due to lack of transportation.
It was never designed to reflect the nationwide popular vote. For the most part it has but that's not part of the design. The decision by the founders to use such a system had nothing to do with transportation.
How is it possible for the electoral vote to produce a different result than the nation-wide popular vote?
It is important to remember that the President is not chosen by a nation-wide popular vote. The Electoral College vote totals determine the winner, not the statistical plurality or majority a candidate may have in the nation-wide popular vote totals. Electoral votes are awarded on the basis of the popular vote in each state.
Note that 48 out of the 50 States award Electoral votes on a winner-takes-all basis (as does the District of Columbia). For example, all 55 of California’s Electoral votes go to the winner of the state election, even if the margin of victory is only 50.1 percent to 49.9 percent.
In a multi-candidate race where candidates have strong regional appeal, as in 1824, it is quite possible that a candidate who collects the most votes on a nation-wide basis will not win the electoral vote. In a two-candidate race, that is less likely to occur. But, it did occur in the Hayes/Tilden election of 1876 and the Harrison/Cleveland election of 1888 due to the statistical disparity between vote totals in individual state elections and the national vote totals. This also occurred in the 2000 presidential election, where George W. Bush received fewer popular votes than Albert Gore Jr., but received a majority of electoral votes, and the 2016 election, where Donald J. Trump received fewer popular votes than Hillary Clinton, but received a majority of electoral votes.
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More states are going to go porportional in the EC; CONs fought it in Maine, and Nebraska but were defeated.