Corrected entry: Dr Strange doesn't have his sling ring on in many scenes of the movie. His first film explained that it is an important tool for a wizard to open up a portal or conjure a weapon. When Strange confronts Thanos for the first time, he challenges Thanos with a dialogue, a close look at the scene will reveal that the sling ring is missing from his fingers, also during the team fight against Thanos the ring is visible in some shots and not seen in others. (01:48:04)
vinoth2803
12th Oct 2019
Correction: The sling ring is not always worn on the hand. It is kept on the belt when not being utilised at that very moment. For him to perform a number of incantations, Doctor Strange would need to remove it to allow for his hand movements.