A quirky language might slow a learner's momentum by making it necessary to explain all the quirks. As a simple example, javascript's rules for casting values t

A quirky language might slow a learner's momentum by making it necessary to explain all the quirks. As a simple example, javascript's rules for casting values to boolean is quirkier than scheme's rule in the sense that scheme's rule ("#f passes conditional tests, everything else fails") is shorter to explain than javascript's rule ("NaN, false, 0 etc fail conditional tests, except new Boolean(false) passes it, etc"). As an experienced javascripter I've grown used to the quirky parts of JS, and some of the quirks are even rather convenient; however it's that much more that needs to be explained to the beginner that isn't strictly necessary.