The person who wants to leave should not have to create a crisis to make the choice believable.

Wanting out is often treated as insufficient grounds. So people wait until things are unbearable, or manufacture a final incident, because a plain preference feels like it will not survive being questioned by others or by themselves. The truth is that a job or a group or an arrangement can be perfectly fine and still not be where you want to spend your years.

If you are considering leaving something, practise saying the reason without exaggeration. It no longer suits me is a complete sentence. Let people be disappointed if they are, and resist the urge to hand them a disaster to make the decision respectable.