Is it reliable to use and download libraries needed from GitHub and copy-pasting codes in order to increase productivity?

I'm just wondering. Is it okay or true that some of the best programmers once taught that to become an effective programmer is through being a lazy programmer rather than spend time memorizing lots of code and get through to deadlines? For example, a programmer relied on research and downloading libraries needed for his or her project, read some instructions or document on how to use the library, and then sometimes whether he or she knows the math will copy-paste the samples. Afterwards, he or she will review its structure's source on how this code used it. Some contribution for help and tips in effective programming to complete the project's deadline would be much appreciated.