A plan usually does not survive contact with reality.
But without one, you are missing the greater context within you choose to act.
And since reality always offers unlimited potential options you would quickly find yourself in a part of reality very far away from your original intentions.
Maybe that part of reality is really nice, but maybe you’re missing out on a much nicer place at the end of your original trajectory.
Grounded on a solid motivational foundation a plan provides a framework of informed and rapid decision making.
In other words: any plan without a proper introspection into the reasons is not worth even thinking about.