Hakuin Ekaku placed extraordinary emphasis on direct realization, insisting that genuine awakening arises from an immediate seeing into one’s true nature rather than from conceptual understanding alone. Central to this was the dynamic of “great doubt,” a profound existential questioning that he regarded as the engine driving breakthrough experiences. This doubt was not mere skepticism, but an all-consuming inquiry that stripped away complacency and forced the practitioner to confront the roots of self-clinging. Within this framework, enlightenment was understood as accessible to all beings, grounded in the inherent Buddha-nature that could be uncovered through dedicated effort. Yet he also stressed that an initial awakening, however powerful, was not the endpoint; post-satori training and continuous practice were indispensable for deepening and stabilizing realization.

To catalyze such realization, Hakuin revitalized and systematized kōan practice, treating kōans as living instruments that cut through discursive thought. He arranged a large body of kōans into a graded curriculum and became especially associated with the famous challenge, “What is the sound of one hand?” which epitomizes the use of paradox to exhaust the calculating mind. This rigorous kōan work was never meant as an abstract exercise, but as a crucible in which great doubt, great faith, and great determination converge. Seated meditation (zazen) and kōan inquiry were thus woven together as complementary disciplines, each sharpening the other and directing attention back to the mind’s original nature.

Hakuin also taught that realization must be embodied in the midst of ordinary life, not confined to the meditation hall. He rejected purely intellectual or quietistic approaches, urging practitioners to integrate insight with daily activities and ethical conduct. Study of scriptures and classic Zen texts had its place, but only insofar as it supported and confirmed direct experience. In this way, wisdom and compassionate engagement were not two separate paths, but a single movement: as understanding deepens, it naturally expresses itself in disciplined behavior, gratitude, and service to others. For Hakuin, the measure of Zen lay in how thoroughly practice permeated one’s actions, speech, and relationships.

Recognizing the strain that intense practice can place on body and mind, Hakuin further emphasized the cultivation of physical and energetic balance. He developed methods that included breathing and other exercises to calm and strengthen the vital energy, aiming to prevent or remedy the imbalances he associated with “Zen sickness.” Such techniques were not pursued for their own sake, but to support sustained inquiry and clarity. In this holistic vision, rigorous kōan-based zazen, great doubt, continuous training, and care for bodily health formed an integrated path, shaping a style of Rinzai Zen that is both exacting and profoundly life-affirming.