次 pairs 欠 (a figure exhaling) with two marks — early senses cluster around stopping over, taking one's turn in sequence. From 'next stop' came 'occurrence': each time is a stop along the way.
次 counts life's repetitions: 第一次 (the first time — a phrase with its own emotional weight in any language), 上次/这次/下次 (last time / this time / next time — the trio that schedules all Chinese social life), 三次 (three times). 下次一定 ('next time for sure') is the internet's beloved gentle excuse. As 'secondary' it grades things: 其次 (secondly). Every repetition, ranked and counted.
Stops along the journey, each one counted — a TIME, a TURN.
下次一定 'next time, definitely' — the polite eternal postponement, canonized as a meme.