How does one become a critical thinker?

Inspired by crisw’s answer in another thread.

Is the ability to be a critical thinker something that has to be taught (or sought)? Does it come about naturally? Maybe with life experience? How did you become a critical thinker?

Is it different for different people? Are some people incapable of critical thinking? If everyone is capable of it, do some reject it purposefully? If so, why?

Critical thinking