> A new language / style / technology / whatever very often will leave us less competent.

This may be a big factor in rejecting unfamiliar languages. Over time the brain trains itself to grok a specific syntax, and understanding becomes partly automatic: we look at a Java program and our brain injects meaning into our consciousness. If we then look at APL or Lisp, however, that training on Java doesn't apply and the automatic injection doesn't function. We're left having to read the symbols directly, and it's unsettling not having the auto-assist. It makes us feel we "can't" understand the language, when it would likely take a couple weeks of immersion to change that impression.