"Whenever you consider there is bliss, and the objective conditions for bliss occur, if you fall under the control of that by becoming arrogant or conceited, then that will fester as an obstruction to the spiritual path. Rather than thinking about what has caused this happiness, which most probably is the accumulation of merit or the removal of obscurations, as soon as the bliss occurs, you think, ''That's my nature." Based on that, you become arrogant or lazy, thinking, "Well, I've accomplished it." This is the greatest obstacle to the spiritual path. This is what creates the realms of deva-gods. Often at times, it is said that people can handle only a little bit of felicity, but they can handle a lot of adversity. This is because happiness on the spiritual path is the most difficult thing to handle. Once it arises, that's where the path stops.
"This does not mean that it is necessary to give it all up. Giving up happiness is not the practice. The main point is not to become mesmerized by happiness as the end result. You realize that, "Ah, now, the good quality of this is that I am fortunate, and this is another result of the great fortune of the path and the result of the accumulation of merit and wholesome deeds. Even more than ever, I will carry on with the work at hand to achieve liberation from cyclic existence." So with more diligence and more courage, you continue listening to teachings, contemplating, meditating, and appreciating this precious human rebirth.
~ from Meditation, Transformation, and Dream Yoga by Venerable Gyatrul Rinpoche, translated by Sangye Khandro and B. Alan Wallace, published by Snow Lion Publications