Let's face it. Project budgets are always tight. No one can develop the perfect cost estimate that covers every conceivable risk, and if you could, it would be too costly to implement. Problems are going to happen in the course of any project, and unless you have a contingency fund to manage those problems, you will have to go back to management for more money with every issue that arises. As a project manager, you should factor some of those problems into your estimate and request cost contingency to allow you flexibility to solve your problems within your overall budget.