Said no to a "quick addition" for the first time and the world didn't end
A PM asked for "just one more field" on something I was about to ship, framed like it was nothing. Old me would've said sure and quietly eaten the extra two days. This time I said it wasn't scoped for this sprint and could go in the next one, expecting some pushback. Got a "fair enough, next sprint then" and that was it. I'd built up this whole story in my head about what pushing back would cost me and none of it happened. Wish I'd tested this a year earlier instead of assuming.