Sometimes you just get lucky. As it looks so far, Zack Martin is a top 5 guard. Shazier isn't anywhere near a top 5 LB as of right now. In fact, I think Zack Martin is the best player of the 2014 draft so far.
The player I really wanted the Cowboys to take was Beckham Jr. The Cowboys draft war room was pretty upset when he went off the board.
And the Lions could have had Beckham Jr, Donald, or Zack Martin and instead, took TE Ebron. Major failure on their part. Three of their DL are FAs this year and may walk. WR Calvin Johnson is nearing the end and may be a cap casualty. And their OL could have really used Martin this year. If the Lions draft either Beckham, Martin or Donald, I think they walk into the super bowl this year.
A lot of the draft is just plain luck. If the Cowboys would have lost the coin toss with the Ravens, Martin would be a Raven today.