How can you change someone's fundamental attitude if fear doesn't work? I'm not sure you can and I'm not even sure fear is all that effective in the long term. Either they want to develop themselves, or they don't.

Some people are just afraid of learning, or never discovered that it could be more than grinding away for a boring teacher. Or they are afraid of falling behind at the "real work". You could try to help these folks with enthusiasm and gently leading through the learning process. If it works, great!

Other people probably have a combination of low IQ and highly-focused attention [1]. Most of this is probably genetically determined; there is nothing to fix, although it will continue to improve into their mid-twenties. These folks are perfectly useful, and even trainable, but management must understand their cognitive limits. They are not so good at solving problems ill-suited to their existing mental tools, and even worse at recognizing the possibility of other approaches. Higher-order systems are probably especially difficult for them. Understand that they can exude confidence even when walking straight into an architecture tar pit. Do no let them drive the high level strategy, and fire 'em if they try to dominate the discussion.

[1] The converse of attention deficit "disorder".

EDIT: fear and activity for the sake of activity create focused attention. An organizational culture of compulsive activity and rapid action can cause this is anybody who buys in to it.

EDIT AGAIN: The opposite of compulsive activity is play. Make a regular game out of trying things just to see what they do.

Bravo, very insightful. Particularly the comment on play.