Something is true, we say, when it actually happened in our physical world.

But some events are even more true than that; so true that they are not limited to a certain year in a certain place. Instead, they occur again and again every year, wherever we are.

They are the days we celebrate every year, in a very real way in our physical world.

See Tanya, Igeret Hakodesh 14. Torat Menachem 5752 vol. 1, pg. 255.