In my experience people vastly prefer their fantasies to reality.

In my experience people demand fantasies, and will fight tooth and nail any encroachment on them by the reality that things never happen as they are planned. Although when I say this, I am thinking of one year and above kind of estimates.

When people who are experts on the topic evaluate the work needed over a period of say 3 months, even in something as notoriously hard to plan as video game production, it can hold. This entails being willing to adjust scope and resources though, when planning, in order to ensure the objectives are likely to be met.

This never worked in 15+ years I've been working. The people who did try that went out the door very soon once management realised some other person could tell them a date and they could plan their business around that date even though that date half of the time got missed anyhow.

Yeah it's tough to get the point across. Worth it if you can, though. For everyone - no-one enjoys rescheduling everything because the deadline was missed again