Look at this way and it will make more sense - you can see your role at McKinsey or whomever as a series of 1 year contracts with a review at the end of each before it is renewed. At each evaluation in an 'up or out' culture the bottom of the intake is culled (sorry to be blunt but its a blunt process), although typically this is more along the lines of 'we would recommend you consider a career elsewhere' etc. Remember that many of the top consulting firms win alot of business from alumni, including those counselled out of the business. Its not as horrific as people imply, although not pleasant. Also as with any firm there are performance metrics you need to meet etc; if you dont make these, you can be fired on these grounds (with reasonable warnings and interventions to enable you to make the grade of course).But as a potential superstar of consultancy, you don't need to worry about this do you? If you are thinking about this before you even start in consultancy, is it really the right career for you?