Crazy doesn't show up in interviews.

“Crazy” doesn’t always show up in interviews. This glib statement is a result of an incident in which I found myself hearing about an employee who, instead of spending his time doing good work for the company, spent time writing numerous preposterous emails to our various departments. With no authorization he posed as a customer in a variety of situations and our very lean staff wasted valuable time as they tried to solve the mystery. Why did he do that, you ask? Indeed. How did he even get hired?  Propensity for aberrant behavior may not always become apparent during the short time that we spend interviewing candidates.
That’s why due diligence when you’re hiring is critical.  Listen to your instincts and perform background checks. Spend quality time with your potential new hires, focusing on not just what a person can do (skills, abilities, talents), but who they are (character, personality, stability) as well.
Hiring well is so important: As your people go, so goes your company.