A detailed plan is useful when you know what you’re doing: when you (or others) have done the thing, or when you’ve been somewhere before. If you know where to go and how to get there a map saves a great deal of time and energy.
But detailed planning is less useful when you don’t know the way: when you’re doing something new, or you’re not even sure where you’re going, or even if the context has changed enough. In cases like this you need to travel equipped with resources and contingency plans. You need to stay alert and responsive to your environment, ask lots of questions, and prepared to change course. In these cases you’ll need a compass to show you the way, but you’ll be making your own path as you go along.
The majority of our most important journeys are more like the second kind.
Use a map where one is available, but don’t be surprised if there isn’t one.