Tonglen is a Buddhist practice that involves taking in the pain of others and sending them relief. Pema Chodron has written an elegant, straightforward article on it here. She describes the process (it's a meditation) of embracing, rather than pushing away, pain as something that "...dissolves the fixation and clinging of ego".
Doesn't this scream Neptune in Pisces? I've written about the highest manifestation of this energy (transcendence, compassion) here and here. But really, tonglen sums it up better than I can. It's channeling Piscean energy. Letting go of your attachment to happiness (and your ego) so you can confront pain. And by confronting pain, you learn that it's not the end of the world. You gain courage for yourself, compassion for others. Note: this is not the same as sacrificing your self esteem. Consider the difference between ego and self esteem. See how slippery Neptune can be?
Just so you know, I've tried this. It's uncomfortable. I fully admit to being attached to my moments of happiness. But I'm currently undergoing a Neptune opposition to my Mars in Virgo so I'm drawn to this subject matter.