Passion projects that actually paid off

With Megaflopolis meeting critical and commercial failure, what are some examples of filmmakers making complicated or expensive choices that actually paid off?

This can be scenes, whole movies, or just aspects of the process.

The one that comes to mind is the shootout in “Heat.” When testing the scene, they used a sound stage, which would have produced a perfectly serviceable scene. Michael Mann hated it, and instead spent 3 weeks having his actors trained by SAS soldiers, police officers, and “casing” the bank they would film at. Then the actually scene itself was shoot on location, using blanks.

Ultimately though, this produced one of the greatest shootouts in movie history.