The motivation and accountability that having a personal trainer provides is invaluable for many people. Not only do you have company along your journey, but there is somebody there to guide you and cheer you on as you work towards a common goal. You should not, however, rely upon your personal trainer to keep you going. Bring your own motivation to the table, and you'll both be amazed at how much more quickly your goals are met.
Having trouble with motivation:
Talk to your trainer about your frustrations and listen to what they have to say
Set short-term goals for yourself
Reward yourself for your achievements
Focus on what you've accomplished, not what you're still struggling with
Write yourself a positive daily affirmation and tape it to your mirror. Whenever you see the note, say your affirmation out loud.