Explaining the slow adoption of new development techniques

From http://idiacomputing.com/moin/FortuneCookies:

Here is Edward Bear, coming downstairs now, bump, bump, bump, on the back of his head. It is, as far as he knows, the only way of coming downstairs, but sometimes he feels that there really is another way, if only he could stop bumping for a moment and think of it. And then he feels that perhaps there isn't.
  - A.A. Milne