One of the peculiarities of software development is how rapidly knowledge becomes obsolete. Dan Appleman cited a parable from Lewis Carroll's Through the Looking Glass which illustrates this wonderfully:

The Queen propped her up against a tree, and said kindly, 'You may rest a little now.'

Alice looked round her in great surprise. 'Why, I do believe we've been under this tree the whole time! Everything's just as it was!'

'Of course it is,' said the Queen, 'what would you have it?'

'Well, in our country,' said Alice, still panting a little, 'you'd generally get to somewhere else -- if you ran very fast for a long time, as we've been doing.'

'A slow sort of country!' said the Queen. `Now, here, you see, it takes all the running you can do, to keep in the same place.

If you want to get somewhere else, you must run at least twice as fast as that!'