Linked URLs returning 404 errors!

I received an e-mail in my inbox from Google Search Console Team informing that 404 errors are in the increase for my other blog. Natural Scientific and Medical Wonders. I checked my blog posts that had been linked with URLs of external websites, and found that the information received is correct. 

As I reviewed more and more posts of the blog, I found that the URLs linked in the older posts were only returned wih 404 errors (not found errors). I am reviewing and correcting each post of the blog.

So, I advise Bloggers to link their posts with URLs of permanent and standard websites only to avoid such shortliving-URLs spoiling the uniqueness of the posts.