Having a personal or fitness trainer helps a lot of people achieve their workout goals. When you go at something alone it is always easier to deter from what you want.
It is very easy to talk yourself into something such as, doing less exercise, eating that extra helping and so on. As far as the exercise goes if you have someone to help you with your workouts you are more likely to work harder. When you have a trainer, they can encourage you and keep you motivated when you are getting tired. Having someone there telling you and helping you get through those last few reps is very important.. Having a person there to talk to and answer your questions also helps.