Responding Well to Counter Offers From Your Boss

How do you decide between taking up a counter offer from your current organization and sticking to your original plan of leaving your job? What does it actually mean when your boss gives you a counter offer? Why do 75% of people look out in the market again within 6 months of accepting a counter offer? When your boss counter offers you with a promotion and career promises, how can you assess the feasibility of that plan and the likelihood of it actually happening?