Those others that reach out to assist many others and who are constantly willing to put lots of time and efforts there and trying many ways to help those persons, even regularly over extended time periods, even though their own lives are filled with much daily minute-by-minute stress, lack of time for themselves, and/or dysfunction, and even though the others may be so different from them, not appreciative of the efforts and/or despite any constant complaints, critiques and self-absorption shown from those others and in not giving reciprocal efforts and kindness back. There are a few on this forum I see as very kind like that.
However, I want to tell those very empathetic persons, although I'm that way, too, as I've done that, been there, and know where you are coming from, frankly I feel you deserve better there, as your time can be better spent than on persons who are manipulative, not truthful or toxic and/or who think life revolves around them and their desires and catering to their every need, with those others thinking your time, wisdom and efforts are nothing, and with them being too narrow minded to want to listen much there, or wanting some magic pill or solution there that works overnight which is some fantasy more than reality.
So, in addition to the mentioned further above, extreme kindness sometimes means to me though eventually backing away from any totally self-absorbed, negative or abusive persons and/or telling them assertively in as constructive way as possible what needs to be said, and not enabling them further in those ways there, so as they can help themselves more rather than think they are not part of the problem, and so as they are less apt to think they are entitled to everyone's time and do not even have to engage or take seriously those that truly wanted to help. So, sometimes extreme kindness too means protecting others in the path of that toxic person.