The news that Randy Gregory has flunked four drug tests in the last year leads you to believe either the NFL has him under surveillance, pee cup in hand, or he's actually a character from an old Cheech and Chong movie.

Whatever the case, the Cowboys should take a lesson from it this weekend while shopping at the NFL combine.

And, no, it doesn't necessarily mean they should focus on defensive ends to use with that precious fourth pick.

What the possession of such a premium pick demands is the surest bet, and not just in terms of talent, either. Consider Jerry Jones' history, if you need references.

Probably shouldn't use the fourth pick on a defensive end considered a top-10 talent with a history of substance abuse like Gregory. This means you, Noah Spence.

No linebacker with an injury history who's already a little undersized for the position like Sean Lee. Looking at you, Myles Jack.

No defensive end lacking sure-fire, big-time pass-rush skills (Greg Ellis) that you settle for because, well, you could always use a defensive end, and you're scared of someone else (Randy Moss).

Is that you, Joey Bosa?

Look, even with all the money spent on talent evaluation, stuff goes wrong. Some players simply can't make the transition from college to the NFL. A team can live with those mistakes as long as they don't happen too often. The Cowboys used up this decade's quota when they traded up to sixth to get Mo Claiborne in 2012.

Even at that, here's the thing: Other than the fact that they used multiple picks to get Mo, the Cowboys didn't hear about red flags from critics at the time. That's really the only good news about the Cowboys' experience with Claiborne. People like me can't say, "I told you so."

Drafting isn't an exact science, but, generally speaking, the higher the pick, the better your chances. The reason this is so is that if there's something you don't like about a player at four, move on to the next one. At that elevated level, there shouldn't be any need to justify someone's history because of his talent, as Jerry so often does, mostly to his peril.

Still, I'm going to give Jerry a pass on Gregory. He took him with a second-round pick, and a late one at that. The kid has a history of smoking weed. Not good. Maybe he can find something else to medicate what ails him. Hopefully something legal. I'm not trying to make any excuses for him. But as second-rounders go, I'd say Gregory's NFL future is brighter than Gavin Escobar's.

Having said that, the fourth pick is too high for someone like Spence, whom Urban Meyer booted at Ohio State after failed drug tests. Then last spring, he was arrested for public intoxication.

This is not the kind of résumé that should gain you entry into the top five, even if you're considered the draft's best pure pass rusher.

If you've been keeping up, you know I've advocated for the Cowboys to take a quarterback with the fourth pick. But that advice comes with the caveat of what they find out this week at the combine and in pro days to come.

They got a close-up of Carson Wentz at the Senior Bowl, and the impression our beat writers came away with was that the Cowboys weren't blown away. Could it be a smokescreen? Possibly. Maybe they're trying to send a message to Cleveland, which picks second. The Browns no doubt are in the market for their 25th starting quarterback in 18 seasons, a dubious streak that includes a pair of Heisman winners (Ty Detmer and Johnny Manziel), a couple of brothers (Luke and Josh McCown) and a guy who won a Super Bowl (Trent Dilfer). Frankly, there were some in there that I'd never heard of.

The Browns' position is a little different from the Cowboys'. They're probably going to go all in at quarterback. Doesn't mean they'll be right, judging by their history. But if they don't take Jared Goff or Wentz or even Paxton Lynch, there may not be anything left when their fans get through with them.

Yes, the Cowboys need to find a successor for Tony Romo, and they have a shot at the best or second-best quarterback prospect in this draft. Does that make it automatic? Only if they believe in him. If they don't think one of these quarterbacks is the guy, then pass.

For that matter, the same applies to everyone else. You have to believe in the fourth pick. If you don't, trade down and pick up another second or third.

And then all you have to do is be right. The Cowboys have done that a little more often lately. They could do it a lot more.

Twitter: @KSherringtonDMN