These features make sats attractive to collect, and periodic events on the Bitcoin network create opportunities for a system of rarity. Different levels of rarity are based on the block in which the satoshi was mined.
Blocks: A new block is mined approximately every 10 minutes, from now until the end of time.
Difficulty adjustments: Every 2016 blocks, or approximately every two weeks, the Bitcoin network responds to changes in hashrate by adjusting the difficulty target which blocks must meet in order to be accepted.
Halvings: Every 210,000 blocks, or roughly every four years, the amount of new sats created in every block is cut in half.
Cycles: Every six halvings, something magical happens: the halving and the difficulty adjustment coincide. This is called a conjunction, and the time period between conjunctions a cycle. A conjunction occurs roughly every 24 years. The first conjunction should happen some time in 2032.