If you've never made a pie, you might not know this, but overworking the dough for the crust makes a tough chewy texture rather than the light flaky texture we all prefer. If you overmix the dough when you're making, say, scones, the same thing happens. Hard, dense, chewy scones instead of light, fluffy treats.
Overdoing it isn't just a problem with dough. Overcook a piece of fish and the proteins seize up, making your fish rubbery, not flaky.
Overdo your exercise routine and you end up too sore to go to the gym for days.
Overdo the celebration at a party and you will feel pretty crummy the next day, whether from too much alcohol or too much food!
Which brings me back to overworking, and a problem that is the opposite of what I typically see with speakers.
Another post on food and speaking, this time from Lisa Braithwaite. Click through to see how the idea is developed.