“Psychologically, you will find it easier to do a single, small piece of a large project than to start on the whole job.”
To perform at your best, you must become your own personal cheerleader. If your inner dialogue is positive and confident, you will be able to easily and naturally motivate yourself. Furthermore, when you focus on what you can do about any situation, rather than wallowing in despair about the negativity of it, you will be able to find solutions and eliminate the problem altogether.
When faced with difficult and seemingly impossible tasks, breaking them down into small tasks, or working on them for a brief period of time, will help you develop the forward momentum you need to complete them.