Passion and interest in your own life.
I have always said I am a "jane of all trades." I have a wide variety of things I liked doing, and things that filled me with purpose. I have tried many things and some have been set down to move on to something else. For me that has been a way of life. When I would read a quote like this one from Julia Child I would think I need to settle on ONE thing and do only it... forever. I don't know if you can imagine the pressure that put on my soul, but maybe you could.
What if I chose the wrong thing? What if I got tired of doing that one thing? What if I lost my passion?
It wasn't until recently I realized that my "something" could be "some things" and that, like other things I had tried, I could let things go if they didn't work the way I thought they should. And sometimes when they work differently they are even better. I don't know...
I do agree with what Julia says. Find something you are passionate about and do it. Stay interested in it and learn more. Do it. And then do something else if your heart leads you in a different direction. That's okay. But do things, and learn things, and be passionate about things, and be interested in whatever it is your hand finds to do.