A lot of the Usual Suspects say that today is All or Nothing Day. Some say that today is a day on which you should remember to live each day as if it were your last. That's not a terrible idea. But none say why today is singled out for this observance. So we move on.
Today was the last day, in 1644, for Blessed Andrew of Phu Yen, the "protomartyr" of Vietnam. (Protomartyr is a term bestowed on the first Christian martyr in any given country. "The Protomartyr," without geographic restriction, refers to either St. Stephen, the very first martyr, or to St. Thecla, the first female martyr. St. Paul had a hand in Stephen's death. It's a long story.)
Blessed Andrew Phu Yen was baptized at 16 by Jesuit missionaries and thereafter worked with them, as an assistant. When the local authorities booted the Jesuits out (the Jesuits have been kicked out of most places they've been), Andrew Phu Yen was arrested. After refusing to renounce his new faith, he was executed. He was only 19 or 20 at the time of his death. He was beatified by Pope John Paul II in 2000.
It was also on this day, in 1948, that President Harry S Truman signed Executive Order 9981, desegregating America's armed forces.