This does not mean that mindfulness happens all by itself. Far from it. Energy is required. Effort is required. But this effort is different from force.
Mindfulness is cultivated by a gentle effort, by effortless effort.
The meditator cultivates mindfulness by constantly reminding himself in a gentle way to maintain his awareness of whatever is happening right now. Persistence and a light touch are the secrets. Mindfulness is cultivated by constantly pulling oneself back to a state of awareness, gently, gently, gently. Mindfulness can't be used in any selfish way, either. It is nonegoistic alertness.