Teenagers think they have forever and old people think they had no time. The truth is somewhere in the middle, and it’s today.

Both ends of a life get the arithmetic wrong, in opposite directions. At sixteen the future looks inexhaustible, and from the far end the whole thing looks like it went by in one afternoon. Neither view is much use, because the only part anybody can act on is the day sitting in front of them.

Skip the large calculations about your life and ask what today is for. One conversation, one piece of work, one thing that would make tomorrow easier. A day is the only unit that comes with a handle on it.