Small confession the first free sample I ever built, I got the main number wrong.

I was so focused on making the dashboard look clean that I didn't double check one of the formulas properly. Sent it over proudly, and the client (very politely) pointed out the total didn't match their own records.

Could've been embarrassing. Instead it became the most useful mistake I've made so far. Now every single project goes through the same rule before it leaves my laptop: does this number match a number the business owner already knows to be true? If yes, I trust the rest. If no, I go back and find out why.

A dashboard that looks impressive but is wrong is worse than no dashboard at all. It just makes bad decisions look confident.