As I was reading about the expression problem [1], I couldn't help but think it sounded very familiar. And then it hit me, I wrote about this nine years ago [2].
This might be another reason why I took some time off [3]—I've already written about a lot of stuff.
Twice this year, I've wanted to write about some topic, only to find I've already written about said topic. For instance, there's this silly [4] series [5] about [6] solving [7] sudoku problems [8] that I've written about before [9] (seriously—I thought this was satire at first, until I realized that this was a serious article by Ron Jeffries, who is a consultant selling this programming methodology).
The second came about because of the alarm clock incident [10] where I was reminded of this weird dream I once had [11].
It's sometimes hard to come up with new material.
[1] http://c2.com/cgi/wiki?ExpressionProblem
[4] http://xprogramming.com/articles/oksudoku/
[5] http://xprogramming.com/articles/sudoku2/
[6] http://xprogramming.com/articles/sudokumusings/
[7] http://xprogramming.com/articles/sudoku4/