If you have grown up in an abusive, toxic or dysfunctional family, it is not uncommon to have learned to put others first.
Sometimes this is because that was the role the person was expected to play in the family, the care-taker, the fixer, the adult.
Sometimes it is because the person saw how unthinking and selfish those in their home environment were and vowed not to be like them, to not hurt others the way they were hurt.
But health is about flexibility. It is just as unhealthy to put everyone else first as it is to think of no one but yourself.
Self-care is important. It is possible to be healthfully selfish. You can take care of yourself and others at the same time.
Learning to find balance can be difficult, especially when expectations and role models have not taught you this. That is why therapy can be so helpful.