What's a learning curve and why is steep not hard?

It's a curve of time versus proficiency.

Steep for hard is wrong because it'd mean that you get very proficient in very little time

proficiency
  |   __
  |  |
  |  |    Proficient in little time (steep = easy)
  |  |
  |_/____________
       time

proficiency
  |
  |       Proficient in lots of time (gentle = hard)
  |            __             
  |           /
  |__________/___
       time

See wikipedia.

"steep learning curve" is a buzz-phrase that doesn't have any actual meaning. It used to mean that you'd make quick progress. "Over time, the misapprehension has emerged that a "steep" learning curve means that something requires a great deal of effort to learn..."

Conclusion: people who use the phrase don't know that it's unclear. You should get details from them on what specific things are hard to learn and get past the buzz-phrases and platitudes.

(from unix.rulez.org/~calver)

_{(source: rulez.org)}

This (very unserious) diagram subscribes to the steep == "hard to climb" interpretation, for anyone keeping score. Emacs. So true. ;-)