Since we spend most of our waking hours at work, how we feel during that time really has an impact on our overall well-being. Our professional and personal lives are not separate from each other and we cannot switch our mood like a light switch. If we are miserable for 8+ hours every day, chances are we feel drained and down in our free time, as well.
In today's job market, changing jobs periodically is a rule rather than an exception. In fact, the rough estimate is that we change jobs 10-15 times during our professional careers. Long gone are the days when you would graduate from college, settle in a stable job, and retire decades later from the same company.