One of the defining images of the modern locker room isn't a fiery postgame speech or a group of guys strategizing -- it's players with their heads down, buried in their phones.

The impact? It's not good.

I've seen the negative impact social media can have, particularly on younger players, who grew up with Twitter and Instagram as an integral part of life.

A player checking Twitter at halftime? I've seen it.

A player tweeting out a grievance with an organization about playing time or how he is being utilized? I see it far too often.

But the most concerning? Watching a really talented player corrupt his mind and confidence by reading all the critiques from anonymous football experts around the world. Negative social media can ruin a player. Reading your mentions? It's poison.

This isn't "Ol' Man Jason" preaching here. Hey, I like Twitter and Instagram -- I'm on both, and they are great for finding articles, reading up, keeping up on breaking news, and staying connected with friends, family, and people you admire and respect. And look at what J.J. Watt was able to accomplish last summer when Houston was devastated by flooding. We're talking millions of dollars for an incredible cause.

But the cons can outweigh the pros in a locker room, especially on this stage. Gone are the days when, after a game, you would immediately call your parents to see how that touchdown catch looked on national television. Now, guys immediately check Twitter and Instagram to see what the world thought. None of us is immune -- we are all guilty at times. But this is what you see:

Twitter

Think that can't affect a locker room? Some of my best-graded games came when my stat lines were not so sexy. Yet to fantasy football Twitter, those are bad games. If you had dozens of people telling you to catch more passes, you're not immune to thinking, "Maybe I should have gotten a few more targets." That's just human nature.

Football is a game where it appears easy to the layman to understand what's going on. If a player puts up big numbers, he's "good." If he doesn't, he's "bad," or he has lost it. The instant reaction to the plays on the field is detrimental to a player who allows the clutter to creep in. Oftentimes in a game, a misread or blown coverage is not what you think it is. How many times have you heard "that cornerback got beat"? On the sideline, the players might know that he was supposed to have safety help. If that cornerback reads his mentions? Ouch.

You just have to stay out of the trap.

These days, many players will react to a summary or clip taken without context about everything that is said about them by a teammate, coach or even worse -- a disgruntled fantasy football owner. That can lead to a grudge and a divided locker room. Note to players when this happens: Talk to your coach face-to-face or tell the captain of your team.

One of my favorite examples of team leadership comes from Derek Jeter and the Yankees. If Mariano Rivera didn't like the hustle or effort from an infielder, he would tell Jeter, "Get your second baseman right." Jeter would handle it. The best locker rooms that I have been in didn't let the noise creep in ... or out. We would handle it internally. If you're engaged in social media, it can become impossible.

Too many times I've seen a struggling player reply to criticism from an anonymous egg with 20 followers, amplifying the situation by introducing it to the Twitterverse. Why? I would always tell young guys, "Keep your eye above the spectator line." As a visitor in any stadium, you hear criticism from the crowd. I remember being in Philadelphia and guys in Brian Dawkins jerseys yelling, "You're getting nothing today, Witten," with a few expletives sprinkled in. That's the norm. But that's also Twitter.

Jason Witten's Social Media Commandments 1. Don't read your mentions good or bad -- the feedback that matters is from your coach and those you respect.

2. Don't reply to a negative; keep your eye above the spectator line.

3. Negative social media is often not indicative of the real world.

4. Use social media as a way to stay informed and connect.

5. Don't post anything that wouldn't make your family proud.

The best players in the league block that out. The mental focus it takes to compete against the best players in the world is not easy to maintain. Developing mental toughness is a learned trait, and if you can't develop it in your pursuit of success, you likely won't last in any competitive line of work for more than a cup of coffee.

We see talented players respond to mentions and get affected by it. That needs to stop. Nietzsche said it best, and I am paraphrasing: "If you stare long enough into the abyss, you become the abyss." I saw it too many times, a struggling player, trying to get back on track, becoming the abyss. I watched a teammate totally get swallowed up by the outside noise.

I experienced it myself throughout my career. Friends and family would read mentions about me which they would start to accept as fact. If our offense was struggling, I would hear the reasons why from friends and family -- reasons that I knew were narratives on social media. Or it was: "Did you hear what [Player X] said about you?" It would drive me crazy. My sole focus was on mastering my craft. The evaluation I focused on? The one from my coaches, who had direct knowledge of the assignment on each play. Teams don't tweet their evaluations to the masses. But now there are scouting services grading the tape and issuing their evaluations when they don't know what they don't know.

The bottom line is: The Twitter mob is not indicative of reality.

Even outside the locker room, the Twitter mob can cause problems. Last year, we saw my alma mater, the University of Tennessee, attempt to hire former Tampa Bay Buccaneers coach Greg Schiano. But Vol Twitter erupted in disapproval, which led the administration to terminate the contract -- and it eventually cost the athletic director his job.

Although many of the young guys coming into the league today are savvy about social media -- they know how to use it, how to engage, and maybe even how to build an audience -- most aren't fully prepared for the coverage and scrutiny. Heck, it was difficult even when we all relied on newspapers, and it is at an entirely new level now with a search of your mentions at your fingertips.

I am a firm believer that playing in the NFL is a beautiful privilege. If you have game, make smart decisions and surround yourself with the right people, you can live out your dream and earn a great income. I love football. It builds character, it can foster lifelong relationships and it can teach you lessons that you can carry for the rest of your life. But what football can give you, social media can far too easily take away.

Bill Parcells used to always say, "There are a lot of exit doors in pro football." And he would have a sign in the locker room as a reminder of all the temptations that can ruin a career. That was in 2003. If Bill were still leading a team today, I can assure you he would be adding social media to that list.