What constancy actually is
There is a stone step somewhere that nobody remembers being installed. Generations of ordinary feet crossed it, and it has worn into a shallow concave dip. No single crossing did that. Nobody pressed harder on any particular day, or crossed it with more intention than usual. All of them together did it, and none of them were trying to.
This is 常 (Cháng). Not discipline in the dramatic sense, and not a streak being counted. Constancy is the quality of something small enough to survive being repeated on an unremarkable day, which is the only kind of day most days are.
Chapter 16 gives this word its clearest setting, and the passage is worth reading in full because it is usually quoted only in part. Attain utmost emptiness, hold firm to stillness, the ten thousand things rise together, and I watch them return. That is where the quotation usually stops. But it is one sentence in the original, and it keeps going: all things flourish, and each returns to its root. To return to the root is called stillness. To return to one's fate is called the constant. Stillness is the state. Constancy is what stillness is called once it becomes the pattern a life returns to, again and again, without needing to be decided each time.
It is worth being precise about which stone this is, since the library now has several. This step is not 和's dry stone wall: that image is about difference held together at one moment, structural fit. It is not 儉's worn tool handle either: that image is about a possession cared for on purpose, maintained so it lasts. And it is not 水 wearing down a canyon, which is geological force acting without anyone crossing anything. The step is none of these. It is one surface, changed by unglamorous repetition, shaped by nobody's intention.
Where Lao Tzu speaks of it
The cost of the impressive start
Most abandoned practices did not fail from a weak beginning. They failed from an elaborate one. The plan was ambitious, the system was well designed, the first week was genuinely impressive. Then the intensity that built all of it ran out, on an ordinary Tuesday, and nothing smaller had ever been prepared to take its place.
The instinct after a missed day is to treat the miss as evidence the whole thing failed, and to stop. But a single crossing was never what wore the step down. It was worn by everyone, none of whom were trying especially hard on any particular day, over a much longer stretch than one lapse could touch. The failure is not the missed day. It is deciding the missed day meant something and stopping there.
常 asks for something almost anticlimactic: choose a version small enough that missing a day does not register as a crisis. Not the ambitious plan, cut precisely and never crossed. The unremarkable version, worn a little more each time, that nobody would find impressive if you described it out loud.
Take one practice you have already abandoned more than once, and rebuild it at a tenth of its original size. Small enough that you would feel slightly silly describing it. Do not count the days. Simply do the small version again tomorrow, whether or not you did it today.