Put on your oxygen mask first is the instruction to parents when being given a safety briefing on a plane before the flight begins. The reason is that if you are unconscious, you can not help your child.
Equally, in day to day life, if you spend your time helping others and not looking after yourself, then you will become depleted, and your metaphorical cup will be empty. If you fill up your cup, then you have more to give.
In order to serve, you must first thrive yourself. To give you must first have plenty. This applies to your health, both mental and physical. To help others, you need to thrive so that the energy you give to others leaves you with energy to take care of yourself, too.
You also see the world and other people through the prism of yourself. You see things as you are, not how they are.