There is a universe in which I don't have to say this.
Where "having the right data" - there's no discussion, it would be insane to do anything without that.
And yet - here we are. I talk to organisations every single day where they struggle to make sure that everyone agrees that the number is right.
I think that this will be my shortest blog post to date - if, ever, you're in a meeting where two or more people disagree about a number: go fix that. Forget every other initiative you might have or be considering.
I wish this was obvious, but getting data right isn't sexy. And so it often takes a back seat to other projects...but it will ruin every other project.
So don't do that: go sort out your data.
Since you're here, a little bonus tip for reporting (it's not about getting the data right, but making it useful): I love "vertical analysis". Basically, on a report, pick something for every line to be a percentage of. Sales, for example. Do that for every report to people outside finance and the C suite - and watch how their understanding improves.