Way back in the day, when Flash websites were still a thing, I was the lead User Experience Designer on a major automotive website. I was young, and had very particular thoughts and assumptions about what made for good UX, and what was utter nonsense.
Then this guy walks into the picture, talking about analytics and metrics, and kept insisting that we need to know what our "measurable objectives" were.
That might not sound terribly mind-blowing to anyone who has used Google Analytics in the last few years, but this was ages before that was a built-in feature. This guy had to the work by hand.
In just one view, my world was blown wide open. I know had access to real data that could tell me how to improve user flow. More importantly, I was equipped to explain to our client WHY we needed to make design adjustments, not based on my own personal best practices, but on real world usage of the platform.
Since that day, anytime I've been able to use data to help clients see the best way forward, there have been no questions about whether my thoughts were right or not. Everything just became a lot simpler.
I leave you with one of my favourite movie scenes: