Bhakti Tirtha Swami
There are only two categories of happy people in the material world: fools and transcendentalists. Fools are so oblivious that they manage to convince themselves that they are happy in this material prison. Transcendentalists are happy because they can see above the material dualities and know that their parole is at hand. Everyone else is essentially miserable. This is because calamity in the material world cannot be avoided, just as water cannot be avoided in the ocean.
Reference: Spiritual Warrior III: Solace for the Heart in Difficult Times, Chapter 6 – A Spiritual Warrior's View of the World
Radhanath Swami
Real Happiness is to love selflessly, being free of anger, lust & greed. In that state we can access the beauty, charm & mercy of the Supreme Lord.
Radhanath Swami
Enduring difficulty for a meaningful purpose is a sublime pleasure.
Srimad Bhagavatam
Any person who is seriously desirous of achieving real happiness (Krishna Consciousness) must seek out a bona fide spiritual master and take shelter of him by initiation.
A.C. Bhaktivedanta Swami Prabhupada
Spirit and matter are completely contradictory things. All of us are spiritual entities. We cannot have perfect happiness, which is our birthright, however much we may meddle with the affairs of mundane things. Perfect happiness can be ours only when we are restored to our natural state of spiritual existence.
Jayapataka Swami
As the materialists are thinking that happiness is all in sense gratification, they don't see the happiness in serving Krishna, that's where the real happiness is achieved in much higher relationship and higher purpose. Their thought is, "Alright Dharma, ardha, kama, moksha" now we will make money, enjoy our sense gratification and at the end of life go for moksha. Howvere in devotional service, we know about prema, the prema is actually the love for Krishna. It is the highest perfection and Krishna is the highest happiness also.