You are totally right everyone have one eye bigger than the other. One of the most famous celebrities once said: you can never find two things are totally the same in the world. Not only are your two eyes different, but also one of your hand or feet is bigger than the other. Although you may see two eyes are the same, in fact, there are always differences between your two eyes. One eye is bigger than the other. The size of our eyes has a close relationship with the orbital bone, soft tissue and the eyelid. However, even in the same person, the orbital bone, soft tissue and the eyelid are totally the same, all those are decided by your DNA. In one word, everyone has one eye bigger than the other.
In fact, everyone's face is not symmetrical. As the growth of age, some people's eyes will gradually become one big and another one small. This situation can be caused by genetic problem mostly. Besides, some people often rub their eyes, also can make the left and right eyes' size different!
Now, it seems most of us have the some sized eyes. But there exist some people with one eye bigger than the other. But this situation is very rare. It is very obviously. It looks weird but they are born with this. Luckily, They can take surgery to adjust their eyes so as to make their eyes look in the same eyes.
The size of eyes generally does not refer to the size of the eyeball in the eye, but the different relaxation of the tension of skin around eyes which indeed cause the different sizes of eyes.
One eye bigger than the other is a practically normal phenomenon which is all the same for the whole human beings and maybe this physiological phenomenon is just little distinct on you. If it affects your appearance, you can go to hospital to have an exact diagnosis and then apply a surgical correction.
Of course it is not uncommon to find some parts of your body bigger than their counterparts. Because there are no identical things in the whole world, you are not going to find the same leaves, right? And there will be no harm, just relax. People are not going to notice that, anyway. But if the one is much bigger than the other one, then it will be awful. Humans are born to have two parts of body, but them are always slightly different from one another.