What is the Brain Drain Phenomenon and how does it impact developed and developing nations?

Brain drain phenomenon takes the best and brightest individuals of a country, mostly in a developing world and due to social, financial and personal ambition, ends up working in a developed nation for a higher QoL ... ends up depleting the developing countries of their best people, further down and proportionally increasing the developed nations power and influence ... while straining their citizens to compete with foreign nationals for jobs, creating problems associated with diversity