Sad for missing the chance to do good
Some people came wanting to join the Prophet’s mission. They didn’t have transport. They asked him, but he had nothing left to give. So they turned away with tears in their eyes. They cried because they couldn’t go and spend for the cause. (QS At-Taubah: 92)
Feeling sad for missing out on a good deed shows love for it. You don’t get sad unless it matters to you.
(from Syajaratul Ma‘arif, Syaikh al-‘Izz bin Abdus Salam)