An audience reaches its limit a lot faster and sooner than most speakers think. The average attention span is only eight seconds. People forget 25 percent of what they hear within 24 hours, 50 percent within 48 hours, and 80 percent in four days. Not long ago, audiences had an attention span of 3.5 minutes. Today that span has shrunk to about 2.5 minutes. That's one reason we now have less time (and less show) between commercials on television.
Your words of wisdom will be competing with people's thoughts of what they did that day, what assignment is due tomorrow, and whether anyone's home to walk the dog. Being brief and concise isn't just polite, it's effective. And it helps you avoid the speaker's ultimate curse: being boring.