There's a natural tendency when people leave to say, "It's them, not us." It's also natural to say, "The best companies in the world routinely prune. Look at Microsoft, Goldman Sachs, GE and McKinsey."<p>The reality is this is a crutch. Firms need to actively remove the weak links, and actively keep the best. If people consistently leave for better opportunities (whether it's more income, more freedom, more responsibility, or all three) then a company is at risk.