Recognising that you are about to experience something that you may not have planned or hoped for is crucial to handling a situation. If you go into denial about what is happening, you will not learn from the experience and will most likely have a hard time overcoming the event.
By identifying what is going on, you will be able to objectively think of a plan of action on how you will solve the situation.
For example, lets say on your summer break you gained more weight than you had anticipated. If you refuse to accept this as a fact, you would most likely just dwell on it with a box of chocolates trying to make yourself feel better.
Definitely not a solution to the problem.
On the other hand, if you accepted that you indulged a little too much and decided now was a great time to get started on the exercise program you've been thinking about, you will find a renewed sense of energy towards your workout, as you know have a goal ahead of you.
By looking at the positive side of the situation, this weight gain will have prompted you to take up the exercise program that will have a whole host of other great benefits for your health other than weight loss- improved fitness.