Why we use Key in flutter widget?

https://apgapg.medium.com/using-keys-in-flutter-1c5fb586b2a5

Using Keys in Flutter

 

I experienced my widget which I want to update doesn't updated and another widget is update. I thoght the reason for this problem is reason why I use same key for widgets. After I use Key(text: String), I could fix my problem.

It would be helpful if you refer to the link at the top.

Enjoy coding with flutter.