By material process, by philosophical process, by mental concoction or mental process they are trying, and Lord Kṛṣṇa also said—they are trying—but that happiness is available when your senses or consciousness are pure. The same philosophy is also Lord Caitanya's philosophy. He says that jīvera svarūpa haya nitya kṛṣṇa-dāsa (CC Madhya 20.108-109).
What is the pure consciousness? Kṛṣṇa said that happiness can be achieved in pure consciousness, or when your senses are transcendental. He gave hint. Not only hint, He practically suggested also that, "You simply surrender unto Me."
So Lord Caitanya said the same thing. Lord Kṛṣṇa said . . . as the Supreme Lord, He commanded—He has got the commanding power because He is the Supreme God—that, "You surrender unto Me." Just like some superior, the teacher or father or king, says: "You must do it." But there is force. The State says: "You must do it," but if you do not do it, then there is force.