Millennials have disrupted the labor market, making it acceptable to job hop and complete "tours of duty" until a better offer comes along. 

In the process, company loyalty has become a thing of the past, and everyone needs to accept it, say Chris Yeh and Ben Casnocha in the Harvard Business Review

We can no longer believe in "this idea that people would go to college, study hard, get a degree, land an entry-level job at a big, stable company." Nor can we believe in the old 20th century compact of employees slowly working their way up the ladder. 

The modern compact is based on alliance. 

"The employer is saying, 'Hey, make my company more valuable, and I'll make you more valuable,'" say the authors. "Even if this is not a relationship that's going to last for an entire lifetime, this is a relationship that is going to be beneficial to both of us during the time it exists and even afterwards."

With loyalty no longer a part of the equation, being an employee in the modern workplace isn't all that different from being an entrepreneur. Uncertainty and volatility is part of the game. There's no guarantee of a promotion or pay raise. 

In a way, that's a good thing. 

"If someone can't be entrepreneurial in their own career, if someone's unwilling to take risks in their career, if someone's not keen on remaining agile and adaptive in their own career, how could you possibly expect them to bring to bear those strengths, those traits at your company?" say the authors.  

To attract and retain the best employees, companies should be more proactive and willing to invest in their workers' future. What's more, they should take a chance on someone who's willing to hustle to get ahead.

Ask not what you can do for your bottom line, say the authors, but what you can do for your employee.