There's a principle I apply to both products and personal finances: the source of truth has to be data, not words.
Why
A customer saying "I'll buy" isn't the same as a customer who has transferred the money. A "paid" click on the interface isn't the same as real cash landing in the account. The feeling "I spent less this month" isn't the same as the number in the spending sheet.
When you let "words" or "feelings" be your source of truth, you make decisions on a wrong picture — and usually only find out when it's too late.
In products
I design systems so that the system itself records the truth: an order only counts as paid when the money actually arrives, goods are only delivered when the status is confirmed. Don't trust the interface — trust the system's data.
In life
This is also why I built the Personal Finance Map: when you can see your cash flow, assets, and goals in one place, money decisions get far easier — because you're looking at the truth, not guessing.
What gets measured gets improved. Let the system tell the truth, then listen to it.