Factual error: In the opening sequence, the camera pans down on a planet and moon that are three-quarters lit in sunlight (with the sun being far off-camera to the left). A battlecruiser then crosses the images as a silhouette, eclipsing the planet and moon in total blackness. Impossible. The battlecruiser should have been lit three-quarters in sunlight, same as the planet and the moon. Stranger yet, as the stormtrooper shuttles are deployed and cross over the battlecruiser silhouette, the shuttles are illuminated. (00:01:55)
Continuity mistake: When we first meet Rey, she is scavenging Imperial wreckage, and she slides down the sand dune on a makeshift sled (she left her speeder at the base of the sand dune, which means she trudged up that massive dune). When she reaches the bottom of the dune, her speeder is casting a distinct, dark shadow on the sand. As she fires it up and rides away, the speeder suddenly casts no distinct shadow on the sand, even after she reaches her destination and parks it. (00:12:00)
Continuity mistake: When Rey unloads the net filled with parts at Niima Outpost, as she picks up her staff to her right we see the black bag hanging on the side of the speeder (note the bag's straps are now much shorter than when she drove off on the speeder), but in the next shot as she continues to pick up her staff, which is now to her left, the black bag is suddenly gone from the speeder (when Rey pulls the net it looks as if the black bag is lying in the net with the parts, though she didn't put it in there), and the net is entirely unattached as well. (00:12:40)
Continuity mistake: When Rey is unloading her speeder bike the sun is setting, but when she goes to trade her gear it's bright and sunny, and when she goes home, in the long shot on her speeder bike the sun's setting again. (00:12:45)
Continuity mistake: After Rey scrubs the salvaged parts clean, when it cuts to Rey standing in front of Unkar Plutt her shoulders are quite a bit taller than the shelf in the wideshot, but in the closeup the shelf is at Rey's chin level. (00:13:15)
Continuity mistake: When Rey is giving the scrap piece to Unkar Plutt, in the wide shot where Unkar says "What you brought me today is worth...", Unkar is holding the scrap piece upwards. The shot changes to a closer shot of the two and suddenly Unkar is holding it sideways. (00:13:20)
Continuity mistake: When Rey returns to her home in the AT-AT she scratches another mark into the wall, and in the next closeup just as she sits down the top part of Rey's outfit is crisscrossed with her left side over the right and her hip bag is at her left side, but after Rey fills her plate and takes her food, she stands up and her top is crisscrossed the opposite way, etc. The first shot is flipped - note the background, compared to the second shot. (00:13:55)
Continuity mistake: After Rey finishes her meal beside the foot of the AT-AT and puts on the Rebel flight helmet, there's an overhead wide shot of the toppled AT-AT and we can see its front knee joint. When Rey hears the commotion with BB-8 she rushes to get her staff, which is now tall and upright in the sand at that knee joint, and had her staff been there in the wide shot we would have seen it. (00:14:45)
Continuity mistake: When Rey reaches the top of the ridge and shouts at Teedo, we see there are no footprints in the sand between her and Teedo, so when Rey rushes to BB-8 her lone set of footprints are the only ones behind her in the sand. When Rey walks away from BB-8 telling him "No," there are many more footprints in the sand between her and the droid, even though there should only be the two sets of Rey's footprints - from both coming and going. (00:15:10 - 00:16:05)
Continuity mistake: When Rey first meets BB-8 there are many footprints in the sand going towards it. When they walk back to the fallen AT-AT, the distance is far greater and Rey's footprints have disappeared. (00:15:10 - 00:16:30)
Continuity mistake: When Rey rescues BB-8 from the scavenger Teedo, the top part of Rey's outfit is crisscrossed with her right side over left, but when she shushes BB-8 it's crisscrossed with her left side over the right. Then it's back to the original way. (00:15:25)
Continuity mistake: When Rey is fixing BB8's bent antenna, at first, the antenna is shown as thin and flexible. But as the scene changes between Rey and BB8, the thin antenna changes to a thicker and slightly more rigid antenna being held between her fingers, then back to a thinner one. (00:15:53)
Continuity mistake: After Rey has fixed BB-8's antenna, she tells him the Niima Outpost is that way, pointing towards the outpost with her left arm. She holds onto the back of BB-8's antenna with her right hand and begins taking her hand off him. The shot cuts to a shot of BB-8 and Rey's right hand is suddenly off BB-8 entirely, down by her side. (00:15:55)
Continuity mistake: When Poe and Finn steal the TIE/SF, both of Finn's torso harness straps have thin pieces of ridged plastic attached to them - nothing else, but when Finn wakes up on Jakku those pieces attached to the straps are entirely different. (00:20:45 - 00:24:00)
Continuity mistake: After the TIE fighter crashes on Jakku, the closeups of Finn waking up and releasing himself from the seat strap while he's lying on the ground are flipped shots. (00:24:05)
Continuity mistake: After getting up from his crashed ejection seat, when Finn sees the smoke and runs toward it his shadow's directly behind him. Just as he reaches the crashed TIE fighter his shadow's in front of him to his left, but when he faces the front of the TIE fighter as it sinks into the sand, Finn's long shadow is still being cast in front of him, even though he's now facing the opposite way, then a thin long shadow is cast onto the sand in yet another direction, to the left of the exploding TIE fighter. (00:24:20)
Continuity mistake: After the TIE fighter crashes on Jakku, when Finn searches for Poe in the wreckage he finds Poe's jacket and grabs hold of the jacket arm, but when it cuts to the following shots as the ground starts shaking, Finn's holding the top (neck area) of the jacket, even though it never left his hand. (00:24:35)
Continuity mistake: When Finn retrieves the jacket from the downed TIE fighter he's standing right in front of it, but when it starts to sink he takes a couple of steps back, then the long shot shows him further away, and even further when it explodes. (00:24:40)
Continuity mistake: After the Quad Jumper blows up, when Rey, Finn, and BB-8 run to the "garbage" they're running quickly toward the Falcon's forward side - note the cockpit, with its entry ramp lowered and nothing blocking its way, but in the next closeup they're all running from the rear of the Falcon before they rush up its entry ramp. (00:31:45)
Continuity mistake: In the scene right after Rey flies the Falcon inside the crashed ship, she cuts the engines and the Falcon begins to rotate nose down, flipping over so that Finn can shoot the TIE fighter down. We see the Falcon falling upside down, then it cuts to Rey slamming the throttle forwards. When it cuts back to the Falcon, it is falling nose first and pulls up, narrowly missing hitting the sand, but is right side up. (00:34:15)
Answer: Any answer would be conjecture - best just watch the next movie.