I have many times faced this problem that including a particular file or CDN twice in a page breaks the functionality of the CDN. The solution is to add it only once per page. Now I want to know the cause for it.
For example, suppose I have bootstrap CDN attached in the index.php page and I have also included the bootstrap CDN in header.php. Now I have included the header.php in the index.php page. I can see as a result the some portion of index.php loses its functionality. Can anyone tell me the core cause behind it? Does it somehow breaks the inclusion thread?
I tried to understand it by including same function twice in a page. But both the page and the function seem to work fine.
I am a little confused and curious about the matter.