At work it is much the same ... when you are not "actively" engaging your brain is when you are most in danger of an "accident". Maybe you lose some business, maybe you get blind sided by a competitor, maybe you miss a business opportunity.
Most people have to work, and most of us are paid to do just that. It is really easy to just fall into the rhythm of a job, each day much like the last and the "glow" long gone. The result is a kind on inertia, I'm pretty sure the brain mass begins to shrink (Kevin Dee's theory ... not scientific fact) and you lose your edge. Your work becomes ... a job! You put in hours each day and slowly (or not so slowly) learn to hate your job. Truth be known if your employer knew where your head was ... they would hate you too!
You DO NOT want to be on cruise control ... in a rut ... spiraling downwards.
You DO want to be engaged, bringing value, stretching yourself, working hard and achieving results. It just feels better, and makes you grow as a person ... and that ability is ALL inside your head!
Think about it ... if it doesn't hurt too much!