As an initial point, you will never be presented with a problem in the workplace that is too big to solve. If it was too big to solve, your employer would not ask you to take on the project. Second, more practically speaking, when presented with a large problem/project it is helpful to break it into smaller pieces. After the project is broken into smaller pieces, it is scheduled and certain parts are delegated out to your colleagues, then those individual steps will appear more achievable, thus, the overall project will also appear more achievable.