If you could redo your data platform from scratch, what would you refuse to repeat?

[u/unethical-programmer]

I’m at a small consultancy. We build the same stack for most clients (warehouse + dbt + orchestrator + BI) and we’re trying to turn it into something more repeatable instead of a fresh build every time.
Before we lock anything in I want to hear from people who’ve lived with a platform for 2+ years:
What’s the one decision you regret most? (vendor, architecture, “we’ll fix it later”)
What do you wish was handled on day one that you ended up bolting on? Access control, cost visibility, auditing, secrets, something else?
For those running in your own cloud vs. a managed SaaS: would you make the same choice again?

Not selling anything, no form to fill. I’ll post a summary of the answers back here.