You cannot get by in the NFL on pure athleticism. In his first NFL training camp with the Green Bay Packers, two-time Pro Bowler Greg Jennings learned the hard way. He recounted the experience in an article for The Player's Tribune:
"In college, quite honestly, I had relied on my athletic ability to beat the opposing corners. I ran a lot of bubble screens, slants, posts. Basic routes. Jump balls. I would catch the ball in traffic no problem. My mentality was, If It's In the Air, I'll Go Get It. 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. 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. 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's one way to learn a lesson.