Good planning doesn't just happen.

"What does the plan say?"  It depends, do you even have a plan in the first place?

Project Managers must take deliberate steps to ensure outcomes for all elements of a project.  The triad of scope/budget/time is fundamental to all projects, but have you also thought about the role of quality, communications, risks, procurement, and human resources?

Many projects run into issues because they lack an understanding of the interplay of all project variables. A good project plan led by a trained project manager will help the team execute and deliver the project.