This was my biggest lesson last year. I used to put people's needs first because I had a hard time rejecting them. Why? Because I felt rejection as well, and it sucks.
I have a huge desire to make an impact, to serve, to move energies around but it took me a lot to learn how to do this in a best way, and at the same time staying in alignment, being energized, feeling satisfaction and joy, without depletion.
The secret is to make a habit of constantly check yourself by asking "how am I feeling now?". "Where is my alignment level". In time you will manage to feel exactly where your limit is, when to stop, and when to give, because yes, we came here to share, to serve, to give, but never to sacrifice and compromise our well being. How can we give sustainably and properly when that happens? How can we give from an empty cup? Always feel your own cup first