Veteran wide receiver Greg Jennings learned early in his career that raw talent and athleticism will only get a player so far in the NFL. In fact talent and athleticism without smarts is a good receipe for post-collision snot bubbles, as the longtime Green Bay Packer (2006-2012) explains in a fascinating essay for the Players' Tribune.

Jennings, who played in Miami in 2015 and is currently a free agent, recalls his "Welcome to the NFL moment" in 2006 as follows:

It took me one play to realize, 'If it's in the air, I'll go get it' wasn't going to translate to the NFL.

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I owe that lesson to Mr. Chris Crocker.

He blew me up. He absolutely, totally blew me up.

It happened in my second preseason game. We were playing the Falcons at Lambeau. I was on the line of scrimmage, getting set. My route was supposed to be a slant.

I take off, make my cut to the middle of the field and turn my head back toward the line of scrimmage. Favre zips it right into the little window. The ball hits me right in the gloves. I have it. I caught one of Brett's bullets. I can do this, man!

Pop!

Before I even feel anything, I hear the sound.

Crocker's playing safety for the Falcons, and he's decided to introduce himself to me. He comes downhill and absolutely blows me up. The ball pops out. I'm on the ground in a heap.

I had never been hit that hard in my entire life. I remember coming to the sideline, and my own teammate, Donald Driver, was like, "I told you, young pup. I told you it was real out here."

That particular play isn't available on YouTube, so use your imagination plus that Jennings-Troy Polamalu shot as a visual aid.

Recently-retired receiver Calvin Johnson opened up last week on the brutality of the sport and the ease of getting painkillers during part of his career with the Lions. In his essay, Jennings also discusses how Brett Favre (at one time addicted to painkillers) learned to play at a high level despite the pain.

Football is certainly an exciting way to make a living but not an easy one.