The answer is in the word breakfast itself, which means the 'breakfast' of a 'fast,' or a long period without eating.
The gap between dinner and breakfast can be up to twelve hours, so the meal that breaks your fast should be healthy and wholesome.
Also, unlike your evening meal, the food your consume for breakfast will give you energy to use while you are active during the day.
There is evidence that eating a big breakfast, particularly one containing whole grains and fruit, can improve your connection and mood, and boost your energy levels.