Planning and Deadlines
Planning is wishful thinking, which is why optimist make terrible delivery estimates. Pessimists are always able to hit the target from afar better.
But fixing an optimist estimate by multiplying by two, is too simplistic. A better fix is something IT departments do all the time: not give estimates. Brilliant buzzwords like agile and sprints mostly allow us to get away with it.
The actual solution is simple: deadlines. You can get philosophical about planning, waterfall, sprints, etc. But if a products has to be live on a certain day, all BS goes out the window, and a minimum viable product plan will appear.
Deadlines are the reality check most plans need. And just like a meeting without an agenda, you should never one without the other.