For me, it was actually kind of boring. Like, properly unexciting.
two things had to line up at the same time: first, the numbers were boringly consistent for ages - same offer, same traffic source, same funnel, same margins, no weird spikes. Second, I got more scared of missing out by staying small than I was of losing money by pushing it.
Mentally, it shifted from "oh god this is working, don't touch it" to "right, if I don't press the gas now I'm just wasting a window." Started with mini scale tests - doubled ad spend and watched CPA hold steady for a couple of weeks. Did that two or three times, nothing blew up, and suddenly it felt less like a leap and more like climbing a staircase.
I've scaled too early before, and that felt completely different - changing multiple variables at once, tracking was a mess, cash flow tight, refreshing dashboards in mild panic every day. That's how I knew I'd jumped the gun.
so yeah, part gut, but the gut feeling comes from seeing the same good thing happen over and over until it feels almost dull. When it's dull and profitable, that's usually your signal