Spend a few weeks reading up on NFL Draft prospects and you'll get used to certain terms being bandied about. It's a kind of shorthand for the draftnik community in many cases, and familiarizing yourself with these terms can help you understand why prospects are highly regarded or generally derided.
One term draws my eternal ire, however. That is "the sure thing" and the "safe pick."
A quick search for "nfl draft sure things" delivers 29.7 million results, with articles calling Khalil Mack the surest thing in the 2014 draft to eight prospects who are sure to shine in their rookies season. Every season, there are a handful of prospects considered to be safer than other players, and a few of them ascend to the "sure thing" strata. I promise I'm done using "sure thing" now.
The reality is that this term is functionally meaningless. Players who are considered to be safe selections or sure bets for NFL success may actually achieve that success at a slightly higher rate than others, but I doubt you could prove that with any kind of accuracy. This kind of rhetoric is littered with the disappointing careers of men like Robert Gallery, Aaron Curry and Jason Smith.
This is not a knock on scouts and draftniks, who are going to miss a high percentage of their predictions because forecasting the pro fortunes of college players is insanely difficult no matter how good your evaluation skills are. It's an acknowledgement that using terms like safe pick is foolish, because prospects of all types at all positions have a chance to bust spectacularly. Teams that try to eliminate risk from their draft processes wind up chasing players with lower ceilings and, at best, a slight reduction in the risk of a player failing at the NFL level. That's not a good way to build a football team.
Remember that there are no sure things in the NFL, much less in the NFL Draft.