Input iterator can be read repeatedly while Output Iterator can only be written once?

I was reading The C++ Programming Language 4th edition by Bjarne Stroustrup. In the iterator chapter (Chapter 31.1.2), it says:

Input iterator: We can iterate forward using ++ and read each element (repeatedly) using *.

Output iterator: We can iterate forward using ++ and write an element once only using *.

I have done many searches on whether input iterator can be read only once or repeatedly, for example: http://www.cplusplus.com/reference/iterator/InputIterator/ https://www.geeksforgeeks.org/input-iterators-in-cpp/

and most suggests that input iterator can be read once only. But why the author says repeatedly for the input iterator? Is this correct? And if so, why input iterator can be read repeatedly but output iterator can only be written once. I always thought input and output iterator are completely opposite of each other.

Thanks everyone!