For all inherent errors, and does not matter who you are or what you are doing. The seriousness of the error depends on the profession. If we take the example of a project manager profession, often errors allowed by new and not yet experienced workers. Ingeneral, we can identify four major mistakes. 

•  The broad scopeof use

 Responsibility for big project gives a sense of importance and prestige. However, the disadvantage of beginners is that they take too many commitments, leading to inevitable failure. Newcomers should not immediately take on large projects. It will be enough to start with a small project, and gradually gain experience. 

•  Interest of sides

The project, by definition, is a group effort, and will be successfully completed when the team will work together harmoniously, listening to each other, decisions will be made unanimously. Error of manager here can be concluded in that, that he can not take into account the views of only someone other. If this happens, it can lead to the erosion and ultimate failure of the project.

•  Wrong targets

Often new project managers fail in their goals because they do not set control targets. Implementation of ideas into something tangible - requires to create a starting point. On the one hand, you can determine how to achieve their goals. In order not to lose the right direction, set the project requirements and keep it to the team at all times. Refer to them when reporting project status. Discuss, whether you, as before are  moving in the same direction.

•  Too much "I",  little "we"

As a new project manager, you can quickly forget that other people are affected by how you handle the project. In many cases, projects are created to meet the specific expectations of stakeholders, so that is an integral part of your planning and management. If you do not know what your stakeholders expect - or worse, who your stakeholders - you're going to disaster quickly.

Project management does not seem difficult at first sight, although it is not so. Even experienced project managers may encounter with problems because many factors influence on the result.
Above all, don`t ignore own mistakes, to learn and had never repeat them.