In reality, there is no eternal happiness nor eternal misery in this universe. What is happiness? Whenever some things happen according to your temporary personal selfish interest(called ego) like getting money, beautiful wife, respect from society, disease free life etc., a person in ignorance call it happiness, while misery is reverse of it that is living in poverty, diseases, old age and early death. So, its clear happiness for a person(in ego) starts with a healthy birth but ends in misery with diseased oldage death, same thing happens for an ignorant animal as well. So, all the material things like body and ego and its associated things like women and gold were never eternal in first place, so how can happiness born from them be eternal. Thats why, scriptures describe truth as "Sat Chida Ananda" Par Brahman Paramatma, a state of eternal bliss, but not temporary happiness.
"Ekam Brahman, Dvitya Nasti"- Brahm Sutras
"There is only one Brahman, and nothing else"
Brihadaranyaka Upanishad 4.4.22 That great, birthless Self
which is identified with the intellect and is in the midst of the
organs, lies in the ether that is within the heart. It is the
controller of all, the lord of all, the ruler of all. It does not
become better through good work nor worse through bad work. It is the
lord of all, It is the ruler of all beings, It is the protector of all
beings. It is the bank that serves as the boundary to keep the
different worlds apart. The Brahmanas seek to know It through the
study of the Vedas, sacrifices, charity, and austerity consisting in a
dispassionate enjoyment of sense objects. Knowing It alone one becomes
a sage/Rishi. Desiring this world (the Self) alone monks renounce their
homes. This is (the reason for it): The ancient sages, it is said, did
not desire children (thinking), 'What shall we achieve through
children, we who have attained this Self, this world (result).' They,
it is said, renounced their desire for sons, for wealth and for the
worlds, and lived a mendicant life. That which is the desire for sons
is the desire for wealth, and that which is the desire for wealth is
the desire for the worlds, for both these are but desires. This self
is That which has been described as 'Not this, not this.' It is
imperceptible, for It is never perceived; undecaying, for It never
decays; unattached, for It is never attached; unfettered It never
feels pain, and never suffers injury. (It is but proper) that the sage
is never overtaken by these two thoughts, 'I did an evil act for
this,' and 'I did a good act for this.' He conquers both of them.
Things done or not done do not trouble him.
Thats why these self-realized Swamis(lord of self) use the word Ananda in their names(like Swami Vivekananda, Yogananda, Dayananda, Shivananda etc.,) and renounce every material thing like family, wealth, wife, sons etc., because nothing is eternal and blissful except real self.
This is what Krishna explained in Bhagwat Geeta, while explaining the importance of Nishkama Karma Yoga(fruitless action) and maintaining contentment in all situations in life. Real eternal happiness comes from renunciation(of ego and material passions born from one's past animal instincts), listen and try to understand Neti Neti-Nirvana Ashtakam
Bhagavad Gita 3.17 But those who rejoice in the self, who are
illumined and fully satisfied in the self, for them, there is no duty.
Bhagavad Gita 3.18 Such self-realized souls have nothing to gain or
lose either in discharging or renouncing their duties. Nor do they
need to depend on other living beings to fulfill their self-interest.
Bhagavad Gita 3.19 Therefore, giving up attachment, perform actions as
a matter of duty, for by working without being attached to the fruits,
one attains the Supreme.
Bhagavad Gita 3.20 – 3.21 By performing their prescribed duties, King
Janak and others attained perfection. You should also perform your
work to set an example for the good of the world. Whatever actions
great persons perform, common people follow. Whatever standards they
set, all the world pursues.
Bhagavad Gita 3.22 There is no duty for me to do in all the three
worlds, O Parth, nor do I have anything to gain or attain. Yet, I am
engaged in prescribed duties.
Bhagavad Gita 3.23 For if I did not carefully perform the prescribed
duties, O Parth, all men would follow my path in all respects.
Bhagavad Gita 3.24 If I ceased to perform prescribed actions, all
these worlds would perish. I would be responsible for the pandemonium
that would prevail, and would thereby destroy the peace of the human
Bhagavad Gita 3.25 As ignorant people perform their duties with
attachment to the results, O scion of Bharat, so should the wise act
without attachment, for the sake of leading people on the right path.
Bhagavad Gita 3.26 The wise should not create discord in the
intellects of ignorant people, who are attached to fruitive actions,
by inducing them to stop work. Rather, by performing their duties in
an enlightened manner, they should inspire the ignorant also to do
their prescribed duties.
Bhagavad Gita 3.27 All activities are carried out by the three modes
of material nature. But in ignorance, the soul, deluded by false
identification with the body, thinks itself to be the doer.
Bhagavad Gita 3.28 O mighty-armed Arjun, illumined persons distinguish
the soul as distinct from guṇas and karmas. They perceive that it is
only the guṇas (in the shape of the senses, mind, etc.) that move
amongst the guṇas (in the shape of the objects of perception), and
thus they do not get entangled in them.
Bhagavad Gita 3.29 Those who are deluded by the operation of the guṇas
become attached to the results of their actions. But the wise who
understand these truths should not unsettle such ignorant people who
know very little.
Bhagavad Gita 3.30 Performing all works as an offering unto me,
constantly meditate on me as the Supreme. Become free from desire and
selfishness, and with your mental grief departed, fight!