IMO (also 30 years in the biz), it's rarely the date, that's #2. it's the budget.

They'll forgive you if you're slightly late, they'll hate you forever if you ask for more money.

Agile works really well if you have a good product owner that has secured appropriate budget for the level of uncertainty in the endeavor & can make decisions and not be overridden by extrinsic forces. Everything else is negotiable.

To me, the _real_ thing that matters isn't quite date or budget, but something that somehow acts as an umbrella to both of them: the promise. When you promise to deliver something by a day, or within a budget, it's very clear whether you met your promise or didn't. However, when it comes to functionalities, there is more of a grey area: you can start to argue that something _mostly_ works, that some bugs are always inherent, or that this functionality actually is not really needed because the problem can be fixed in an operational way, or that the requirements have changed, or that it was just a nice-to-have... but money/time don't have this grey areas.

The corollary is that it's only the budget that is tracked that anyone cares about.

Often your salary is not on that budget, so if it takes you twice as long but you don't have to buy/hire/use AWS, winner.