We often think there is a conflict between exertion and just letting ourselves be there. However, exertion is letting yourself be there, in this case. To experience openness and letting things be, you yourself have to let go, which is the leap or the exertion part. Freedom, or spontaneity, is the outcome of taking that leap. You have to push yourself to let go, to leap into freedom.
From Mindfulness in Action: Making Friends with Yourself through Meditation and Everyday Awareness.