Why is using the std namespace considered bad practice?

Question

C++ / C#

Hello! Why is using namespace std considered bad practice? I study the pros language myself, and even more so, I really like this language. I watched lectures on YouTube that were led by Timofey Kharyanov - it was he who said that using namespace std is very bad, even Björn Stroustrup does not recommend .. I went to google as an answer and did not understand ..

Answer 1

For example, because in the std space there is a shitty cloud of functions declared in the library that you may not even suspect about. And you can name your own function the same way. Without even suspecting that with each call to it, the compiler now doubts which one to use - yours or the library's. And the decision in favor of the library (for example, because you made a mistake in the arguments) will come as a surprise to you.