The fourth renunciation thought is that samsara is unsatisfactory, frustrating, and full of suffering.

Samsara begins with dualistic mind. At the heart of dualistic thinking is ego-clinging: the strong sense of being an “I” who is separate and more important than everyone and everything else.

Dualistic mind is always accompanied by its retinue of the five negative emotions: attachment, anger, arrogance, jealousy, and ignorance. Ignorance, in particular, manifests as doubt and hesitation, and in narrow, carefully guarded intellectual stances.

Dualistic mind puts an enormous amount of time and energy into supporting, strengthening, and defending itself. It judges situations only in terms of its own hopes and fears. It is sensitive, wary, and easily wounded. It is never satisfied.

The activities of dualistic thinking are known as samsara. Samsara means “circling” or “wandering.” This means that no matter how much we think, speak, or act based on the demands of our dualistic mind, we never really get anywhere.

The more effort we put into samsara, the more frustrating it becomes. Eventually we fall into a pit of suffering.

When the Buddha gave his first teaching on the four noble truths, the first truth he taught was the truth of suffering. He taught that suffering is painful, but we can learn from it, use it wisely, and ultimately go beyond it. We can learn from our own suffering to be more compassionate to others who also suffer. We can use our suffering as a catalyst to bring more courage, commitment, and joy to our practice.

As our practice deepens, our minds grow in strength and clarity so that we can penetrate to the cause of suffering—dualistic mind—and transform and transcend it. When we are absolutely free of samsara we can help others become free as well.

The complete meaning of the fourth renunciation thought is that while samsara is painful, it can and should be used for understanding and realization. The Mahayana and Dzogchen teachings say that samsaric situations are agents of our transformation and growth, and that the greatest suffering, when worked with intelligently, yields the greatest realization.

Source: Sherab, Khenchen. The Nature of Mind (pp. 121-122). Shambhala. Kindle Edition.

In a dream, one might be the lord of gods and humans with riches, mansions, and an abundance of everything one could enjoy.
But when one wakes up, there is nothing left. It is as The Way of the Bodhisattva says:
All that I possess and use
Is like the fleeting vision of a dream.
It fades into the realms of memory,
And fading, will be seen no more.
Accordingly, because it is the nature of things to change when we die, we cannot count on any of the superficial happiness of cyclic existence.
So reflect, thinking, “In this present life, I must do whatever I can to obtain liberation from the great ocean of suffering that is cyclic existence and attain lasting happiness in perfect Buddhahood.”
(Dudjom Rinpoche)