Think of soccer or basketball. You get the ball near your own goal (or basket), and you want to dribble it forward. Ideally you have a plan. You’re going to pass it up the side, and from there a play will develop. Or you have some other plan.
And things change rapidly. The opposing players surprise you by doing something different from what you expected.
You watch the play developing. You keep your eyes up to see the field (or the court), but you also focus on the ball and the details of dribbling, probably at the same time.
This is a good example of planning as you go. You watch the field and the details at the same time. You expect things to change. You expect to react to the change quickly.
So it’s not that you don’t have a plan or that you don’t want planning. It’s that you want planning to be very fast, flexible and adaptive. The goals remain the same, but the detailed plan changes.