History proves to us that one vote absolutely does matter.

In 1829 in Kentucky, Nicholas Coleman defeated Adam Beatty 2,520 to 2,519. In 1847 in Indiana, George G. Dunn defeated David M. Dobson 7,455 to 7,454. In 1847 in Virginia, Thomas S. Flournoy defeated his opponent 650 to 649. In 1854 in Illinois, James C. Allen defeated William B. Archer 8,452 to 8,451. In 1882 in Virginia, Robert M. Mayo defeated George T. Garrison 10,505 to 10,504.
The greatest upset in American Presidential history is the 1948 election in which Harry S. Truman defeated Thomas Dewey.

Here's where the power of one vote comes in.
In 1948 there were 9,247 voting precincts in Ohio. Truman won the state by just 7,107 votes. Had just one Truman voter in each precinct voted for Dewey or had one Truman voter in each district decided to stay home and not vote -- Dewey would have won the state and its 25 electoral votes.
The situation in California was similar. There were 16,802 voting precincts and Truman won the state by just 17,865 votes. Imagine if just one Truman voter in each precinct had instead voted for Dewey. Subtract 16,802 votes from Truman's total of 1,913,134 and add them to Dewey's total of 1,895,269. The result? California's 25 electoral votes go to Dewey: 1,912,071 to 1,896 ,332.