As a project progresses from an idea sketched on a white board to a preliminary plan and into a full-fledged project management plan with a schedule and all the bells and whistles, it will gather risks around it like moths gather around a light. Risks will pop up during every phase of the project.
Even the most well-prepared project manager on the most well-planned project will end up dealing with risks. How it affects the project, though, is determined by how well the team deals with those risks.
The best way to deal with risks is to remove them from the project in one way or another. Removing risks can help the project proceed without the distraction and the extra work entailed in dealing with risks left to their own devices. Dealing with any risk involves four key phases. (more here)