Ask HN: How does one gain expertise in scalability?

My experience is mostly in experimental software and prototypes that never made it into production. I have some vague ideas of techniques that are used to scale applications and have read materials such as that on http://highscalability.com, but no practical experience in this area, nor any projects where I can apply any of this information.

For those of you who are knowledgeable about scalability, how did you develop that knowledge?