Although I am an expert in executing HTML and CSS, I am not an expert in the details of the HTML 4.01 and XHTML 1.0/1.1 standards. As such, I have had some strange misunderstandings of how it all works. When compared, XHTML strict is an elegant thing of beauty and order, while HTML transitional is an unholy land of disorder and corruption.
And why not think this way? Whenever I have taken a peak under the hood of a poor looking site, it was in HTML 4 with disordered markup. Whenever I look at a good looking site, it is in XHTML with orderly markup.