I grew up in a rural area. Rural enough that dogs chased cars. Extraordinarily enough, the dogs never caught the cars. In fact, they never got close. It was good sport. The dog felt very fulfilled, barked aggressively and made sure to never come close to catching the car. As best as I can recall, the car was never affected by the ordeal.
How many of us catch the whiff of opportunity, chase after a new opportunity without stopping to consider the ramifications if we get it? I know I've cursed my luck for not getting a position, and jealously watch someone else get sucked down a drain. The ironic thing is how often the first person to win a great opportunity flame out. Either because the lacked the skills or because expectations got so carried away, no one could hope to succeed. That's the dog who caught the car.
So the next time you see that great opportunity and begin bargining your life away, think about whether it's worth the tradeoffs necessary. Think about whether you have the skills and abilities to make the choice pay off. Think about whether you want to be the dog that catches the car.