Why are breasts different sizes?

During puberty, breasts don't always receive identical amounts of the hormone that makes them grow. Why does this happen, and how common is perfect symmetry anyway?

What It Means When Your Left Breast Is Bigger Than Your Right

7 Strange Facts About the Female Body

What is the Ideal Breast Size? - Vanity

Photos Show How Bra Sizes Can Be Wrong

Is It Normal to Have Different-Sized Breasts? - GoodRx

What are the reasons behind increasing the breast size of women after marriage? - Quora

Why Is One Breast Bigger Than the Other?

Asymmetrical breasts are more common - Cultura Colectiva +

Women's General Health

Why do women have two different sizes of breasts? - Quora

Breast changes after pregnancy and during breastfeeding

Even-Stevens - Why Your Breasts Are Different Sizes - Costhetics