Heraclitus wrote: “Upon those who step into the same rivers, different and again different waters flow” (fragment B12). The famous “you can’t step in the same river twice” is a later version. Read slowly, he’s saying something stranger: the river stays the same because the water doesn’t.
That’s the whole collection examined, every room. Now imagine doing this with your own life, for a year, with two people who come to know it well. That’s membership.