Validation is the key to shutting down a complainer initially. 
Do not roll your eyes or check your email. Rather say things like "I hear you." Complainers can wear themselves out in five minutes unless you ignorantly add fuel to the fire by suggesting a solution. Then the complaining will last much longer.

Dealing with a chronic complainer: Listen and nod

Many chronic complainers are not looking for advice even though they want to share their problems.
If they ask for advice, it's best to keep it short and on point. They may reject your help after they ask for it, saying it is useless or irrelevant. As annoying as it can be, recognize that they want to complain. Ask them how they intend to fix their problem?

Keep advice brief and to the point

If it is essential that if you have to disagree with a chronic complainer, you can ask this simple question: "Do you want my opinion?"
The complainer then has to give you permission to share a different perspective, but don't try to convince them. Say "I hear what you're saying, but I see it differently." This way, you won't feed the fire. Once they know how you feel, they'll move on to complaining to someone else.

If you want to disagree, do it right

Chronic complainers genuinely believe the world is out to get them and feel they have to voice every disappointment in their life.
In reality, many chronic complainers are unaware that they complain so much or that they have a reputation for constant negativity. They may even feel they have a duty to alert others to potential hardships.

We all know at least one chronic complainer

<ul>
<li>Validate: Now that you've shown them you're listening, you can deploy the ultimate weapons for shutting chronic complainers down. </li>
<li>Next, it's time to sympathize. Try to make it as authentic as possible. Avoid all sarcasm as they will notice it, and it will cause more problems.</li>
<li>Validation and sympathy are usually enough, but for the really tough cases, respond with deflection without shutting them down or telling them they're wrong. For example, if they're complaining about a person, say "It sounds like you two have something to talk about."</li>
<li>Redirect is similar to deflect. You're changing the subject of the conversation without making it obvious. For example, "The printer jammed on you again? That's so annoying! I know it's hard to shrug off these things, but I hope you can be a trooper because we have to get back to ...."</li>
</ul>

Dealing with a chronic complainer: Validate, sympathize, deflect, redirect

An optimist sees a glass half full of water. A negative person sees the glass as half empty. The chronic complainer sees water that isn't cold enough, sees the smudge on the rim, which means the glass wasn't cleaned properly and wonder if they will end up with some kind of virus.
Chronic complainers may not have a negative outlook on life but they want everyone to know that nothing is ever good enough. In their mind, the world is what's negative, and they are only aware of one way to respond to it. They don't know how to express themselves in a positive light.

The negative person vs the chronic complainer

You can't change somebody's behaviour, but you can control how you handle them over time.
<ul>
<li>Don't ever tell them that things "aren't so bad" as this gives the message that you're not taking their pain seriously.</li>
<li>Don't ever complain about the complainers (or with them). If they find out that you complain about them, you'll have a chronic complainer that also dislikes you - indeed not a good combination. If you join in and complain along with them, it increases the likeliness that their problem will never be solved.</li>
<li>If it gets too much, draw the line. Tell the person that you like them, care for them and want to support them, but that you will no longer listen to how bad things are. Be sure to reward a change of behaviour by thanking and appreciating them.</li>
</ul>

We all know at least one chronic complainer

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