A decade after its debut, one Blue Bloods season 1 casting choice still has many fans scratching their heads, and that's Sami Gayle's Nicky Reagan. Whether they've been there from the show's start or jumped on the bandwagon after a binge-watch, viewers can't quite get over the fact that Gayle didn't always play the daughter of Bridget Moynahan's assistant district attorney Erin Reagan.

While Gayle has played the smart and mature-beyond-her-years Nicky since the first season, she wasn't actually the face of the Reagan family's second Columbia University graduate in the show's pilot episode. Dan in Real Life and Law & Order actress Marlene Lawston originally played Nicky Reagan in her last recorded screen role.

As Lawston and Gayle have little in common in terms of their look, it's hard for fans not to wonder when watching the pilot versus the rest of the series.

One Reddit user noted that while they weren't sure why the actress had been recast, the dramatic difference in their appearances was frustrating. "I don't know what happened, but could they really not find a closer lookalike actor?" u/Kell08 wrote.

In the years since the casting swap, CBS hasn't commented on why they made the change, and neither have any of the show's creative talent, leaving many fans to reach out to their local TV columnists with questions about what happened behind the scenes (via Fosters).

While the recasting might seem odd, it's actually not all that uncommon. There are plenty of reasons — from narrative changes to cast chemistry — that could have been behind why Nicky Reagan's actress was replaced.

Acting quality or standard casting procedures may have been behind Marlene Lawston's Blue Bloods recast

If you're a lover of television, Nicky's Blue Bloods recast is probably not your first rodeo when it comes to actor-swaps. Game of Thrones, Gilmore Girls, 30 Rock, New Girl, Golden Boy, and many other TV series have recast actors, especially after their pilots have aired.

That's because pilots act like story pitches, and those can sometimes be flawed in the rush of pilot season.

After these first episodes are cast and filmed, they're presented to network executives to evaluate various elements of the completed episode. Sometimes, executives like a lot about a show but take issue with a single actor's performance. It might not be strong enough or even the right delivery for the studio or network leadership. It could also be that the performance is perfectly fine, but the show's creative team has found that the actor doesn't quite "vibe" with the rest of the cast.