What are the social and professional implications of plagiarism? Why would someone risk their professional reputation and credibility by plagiarizing?...

What are the social and professional implications of plagiarism? Why would someone risk their professional reputation and credibility by plagiarizing? Is it always intentional and if so, what are the ramifications of unintentional plagiarism? Can "accidental" plagiarism ever be proven?

please provide references, thank you in advance