There are often enough times when we give our all to help others unconditionally, receiving no gratitude and sometimes even ugliness in return. Regardless, all these received negativities do not pull us down, because our intention is to help unconditionally to make lives better without even for a moment thinking of returns.
The 'high' of giving unconditionally, even when to the extent of sustaining damage to ourselves from received ugliness and/or working beyond humane limits - this 'high' at the end of the day makes it all worth it, and gives us the strength to continue to give tomorrow.