The main idea of "Where Monsters Can Grow" is that monsters can grow in unexpected places, and can take many different forms and shapes.
The author explores the idea that monsters are not always the scary, supernatural creatures that we typically associate with the term, but can also be everyday things that we fear, such as illness, loneliness, or change. The article suggests that by confronting and accepting our fears, we can overcome them and learn to see the world in a different way.
Overall, the main message is that the things that we fear can become less monstrous if we are willing to face them head-on.