By Carolyn O'Hara,

No one likes picking up someone else’s slack. But when a colleague leaves early, misses deadlines, and doesn’t give 100% to a project, it can be difficult to determine the best course of action. Should you confront them about their behavior? Speak to your boss? Or mind your own business?

What the experts say
We’ve all worked with someone who doesn’t pull his own weight — a colleague who checks Facebook all day, takes two-hour lunch breaks, and never meets a deadline. But as irritating as it can be, you shouldn’t become the behavior police unless their slacking is materially affecting your work. “You don’t want to have the reputation of an oversensitive alarm detector,” says Allan R. Cohen, a professor of management at Babson College and author of Influence Without Authority. Susan David, the founder of the Harvard/McLean Institute of Coaching, agrees: “If your slacking coworker isn’t impacting your ability to do your job or your ability to advance in the organization, move on and focus on your own work.” But if your job is suffering because of your colleague’s behavior, it’s time to act. Here’s how to handle this tricky situation.

Put yourself in their shoes
Dealing with a colleague who isn’t giving his all can be frustrating, but don’t presume to know the root causes of his behavior — slacking doesn’t always indicate laziness. “It may be an issue at home,” says Cohen. Or it could stem from difficulties at work. Perhaps the person is struggling to understand a new assignment or to learn a new skill set. “Context matters,” says Cohen. “You don’t want to make assumptions about the other person’s motivations.” He advises doing some “exploration and inquiry” before making any moves. And that includes some introspection. But don’t spend too much time debating whether to approach them. If you wait until you’re fed up with their behavior, you’re more likely to lose your temper and look unprofessional.

Choose conversation over confrontation
If your work is affected by your colleague’s behavior, it’s time to speak up. But don’t ambush him or adopt an accusatory tone. “Approach the conversation with curiosity and compassion,” says David. “You want to show that you’re genuinely trying to solve the problem, rather than punish or make a point.” Ask how things have been going. Say, “I’ve noticed that you seem to be less engaged with this project than you used to be. Are there ways that I could help?”

Stick to the facts
Bring specific examples of the offending behavior to the conversation, and clearly explain the impact it’s had on you and other colleagues. “You want the discussion to be, ‘Here’s what happened and here’s the difference it made,’” says Cohen. For example, tell the person that her missed deadline jeopardized a client’s deal, or that her early departures required you to stay late. But keep the dialogue positive and forward-looking. Cohen suggests role-playing the conversation with someone first to get the words and tone right.

Be flexible
You may have your own idea of how best to fix the problem — but don’t get fixated on any pre-set solutions. “What is helpful is to explore different options with the individual,” says David. You should also resist the temptation to think about the situation as black-or white:  you’re right and the other person is wrong. “Thinking someone is wrong is actually very depleting to us as individuals,” says David. It takes up energy, and “prevents our ability to solve anything.”

Give them a second chance
If one conversation doesn’t do the trick, try again. It may be that you weren’t direct or specific enough the first time. “You want to be able to come back to the person and say, ‘We talked about this, here’s what you said you would do, and here’s what hasn’t happened,’” says Cohen. “There might be a couple rounds of that.” If the behavior persists and it continues to negatively affect your work, it’s time to take the issue to your boss. But give your colleague a heads-up, Cohen says, both out of professional courtesy and as a further spur to change his behavior. “I believe in advance warning,” he says.

Tread carefully with your manager
Approach the boss in the same way you did the slacking colleague: with empathy, an open mind, and specific examples. If you handle the situation with grace, your manager will be impressed. If you don’t, you “start to be the person who is toxic, and who doesn’t have the emotional agility to move on,” says David. So make sure you come across as flexible and willing to help solve the problem.

Principles to remember

Do:

* Keep an open mind — your colleague might have unseen reasons for slacking

* Address the issue with your colleague before talking to your boss

* Use specific examples to show how the behavior is affecting everyone’s work

Don’t:

* Get caught up in the issue — if it’s not affecting your productivity, it’s not your problem to fix

* Tell your boss without giving your colleague more than one chance to improve

* Use an accusatory tone — approach the conversation with curiosity