Continuity mistake: While Tony and Peter talk in Thanos' ship, Peter's hair changes between shots.
Continuity mistake: Before Heimdall sends Hulk to earth he moves his hand between shots.
Continuity mistake: Just after Tony realises Drax isn't listening to him, Star-Lord tells Tony not winging it isn't really what they do. In this shot, Tony is looking at Star-Lord. Spider-Man asks what exactly is it that they do, and Tony is suddenly looking at Spider-Man, then Mantis says "Kick names, take ass" and Tony is suddenly looking at Drax and Mantis. (01:22:25)
Continuity mistake: When the armies are approaching the barrier in Wakanda, in the shot where M'Baku is first chanting with his army, T'Challa is approaching him and Captain America, Black Widow and Bucky are a couple of feet next to him. When they stop, Captain America is standing ahead of Black Widow. It then cuts to T'Challa saying "Thank you for standing with us", and Captain America, Black Widow and Bucky are now side by side. (01:37:40)
Continuity mistake: When Thor, Rocket and Groot begin charging towards the army after arriving in Wakanda, the shot from behind them shows Rocket and Groot running slightly behind Thor. Then it cuts directly to a shot in front of them, just before Thor jumps into the air, and Rocket and Groot are now further back. (01:45:50)
Continuity mistake: When casting Thor's axe, the forge is barely tilted when the molten metal begins to pour, indicating it was almost full of material. But, in the previous shots, it is not, even after the bars melt.
Continuity mistake: In the close up shots of Thor when Thanos has his hand on him there is blood coming out of his mouth. In the long shots though there is no blood. (00:02:54 - 00:04:04)
Continuity mistake: Thanos reaches down and picks up Thor by the collar of his uniform. Thor is facing head first with his back parallel to the floor. Thanos lifts him and walks towards Loki. In the next shot of Thor he is now sitting upright and Thanos has his hand on top of his head. (00:02:22 - 00:02:54)
Continuity mistake: While Iron Man talks with Thanos on Titan, Tony's facial hair changes color and amount.
Continuity mistake: Thanos stabs Heimdall in the chest but the spear is taken out from his stomach.
Continuity mistake: When Black Widow stabs Corvus Glaive, she kicks him to the ground and he drops his weapon, with the weapon landing beside him. Proxima Midnight then runs up to Black Widow and Captain America picks up Corvus Glaive's weapon, but it is now much further away from him. (00:41:05)
Continuity mistake: Whilst they are discussing the plan on Titan, just after Star-Lord tells Tony to not call them plucky, the shot cuts to Tony turning his head to Star-Lord. In this shot, Tony and Star-Lord are positioned around 90° rotated from each other, but in the next shot, the two are suddenly facing each other directly. (01:22:55)
Answer: "Doctor Strange" demonstrates that the Infinity Stones are useful in the most dire of situations, when Strange used the Time Stone to prevent Dormammu from taking over the Earth. It's also possible that some of the stones are indestructible. Wanda is able to temporarily destroy the Mind Stone by using her own powers, but the Power Stone will destroy any being that doesn't possess the strength to wield it, and the Reality Stone is shown to have a will of its own and defended itself when it bonded with Jane Foster.
Phaneron ★
Also, in the comics, if the stones are destroyed they will simply be replaced by something else or even stones again. They represent the existence of the universe and cannot be destroyed for real. Always only temporarily.
lionhead