Brain drain sounds like that feeling you get at 4pm on a Friday. The coffee's not working, the week's almost over, and your focus is fading fast. Or could it be what happens when you meditate - draining your mind of all worries and thoughts? Actually, it's neither.

Brain drain happens when large groups of skilled workers leave an industry, company, or geographic area at once, draining it of human capital. It's a silent killer that can tank innovation, negatively affect performance, and destroy employee morale. Here's what causes brain drain, how it affects organizations, and what you can do to stop it in its tracks.