Design (and test) for 10x your current scale, build for what you need now. And the system has to be able to handle peak loads, and if you don't know what those are build in a safety margin or a way to shed or defer work if you need to.
Everything is a tradeoff, optimize for the things that need optimizing, and determining what those are is the hallmark of a good engineer.
I've found the same. You should understand what your 10x / 100x growth solution would look like (assuming that that's relevant - obviously if you have no intent to hit that scale, don't bother). Build your system to handle your 1-1.5x, maybe 10x scale, and make sure you're not blocking the 10-100x solutions by doing so.
Everything is a tradeoff, optimize for the things that need optimizing, and determining what those are is the hallmark of a good engineer.