When we talk about 'nothing lasts forever'... we're also talking about the worldly happiness, great fortune, and all the things that our mind perceive as pleasureable... that too don't last forever.
The Dharma that was preached, if practiced, breaks all worldly perceptions that we have. The things that make us happy or sad, angry or pleasured... are all works of the mind. As any of the two opposites will can turn on us anytime, what we experience is not reality in the first place... just an illusion built by our mind.
I'm a practitioner of the Dharma, still practicing... I have not yet acheived a mind devoid of personal perception. But looking at how the Dharma has helped countless of people to break free of the mental entrapment we've crafter ourselves, is comforting. At the same time, it builds my confidence and keep my faith still in Dharma. For this every reason, I constantly read biographies of great lamas and stories of the Mahasiddhas. They're really great.