What tells you a product is becoming a habit?

What tells you a product is becoming a habit, rather than just getting a second visit out of curiosity?

I’m trying to separate the signals that look good in analytics from the ones that reflect a real change in someone’s routine. A return visit is encouraging, but it can still be a quick check. The stronger signs seem to be when someone repeats the same workflow without being prompted, brings the product up while solving a related problem, or notices when a small part of it changes.

For people who have watched an early product find repeat users: what was the first behavior that convinced you this was real? Did you measure it as a time window, a repeated action, or something you only noticed in conversations? I’m especially curious about products used weekly or less, where “retention” is hard to read.

I run IndieNeed, a directory for indie products (https://www.indieneed.com/submit), and this question is making me think about rediscovery as part of habit—not just acquisition.