(a logo is) a simple tool, like a hammer; it has a straightforward function. Anything that gets in the way of that function weakens the effectiveness of the tool. Keep it simple. Same for symbols. Simplicity, clarity, elegance. And by elegance I mean the sort of form that a wide diversity of viewers will find visually active and easily remembered. Being memorable matters a lot. If the form is ornate, it can't stick in memory. Simple and ugly is easy; simple and boring is easy; simple and vague is also easy.
That's one reason I aspire to logo design. CreativePro.com has an excerpt from the above New Riders book (which is where the quote comes from) which you can download (it's a PDF) via the article at this link hyar.