One of the great things about iron is that you can depend on it to keep its shape. If you do want to bend it or shape it, you must go through the difficult job of heating it than pounding it into the shape you want. Then, it is relatively easy.
To Strike While the Iron Is Hot is to act when you have the greatest chance of success (like a metal worker with their hot iron).
For example, the student heard that his mentor would only be in town for one day. If he wanted to meet her, he would need to hurry down to the lecture and strike while the iron was hot.
Heard any good idioms lately? I take requests. See you tomorrow.