Jace, sweetie, apple of my fucking eye, find all the chairs and sit the fuck down and shut the fuck up! I swear to the great googly moogly above that Jace Wayland has a brain of an ant, he’s so fucking dumb. It’s very clear that Clary and Jace are meant to be together, because they are both dumber than a mountain’s worth of rocks.
The mortal cup is fucking important, it can make or break your quest to retrieve Jocelyn. Not only that, The Mortal Cup is one of the two ways in which Shadowhunters are made. If destroyed the cup would have a massive determinantal effect on the survival of your entire sub-species. To put it plainly: the destruction of The Mortal Cup could mean the end of the Shadowhunters. And the only obstacle you have to achive your goals is that you to get passed is Dorothea. Yet, instead of being nice and convincing her to give the cup to Clary. Jace is going to just be a complete asshole and fucking insult her.
I said it once, I’m going to say it again: What a complete and utter fucking dumbass !
This is the prime reason why Alec was right, and Jace should have stayed back at the Institute. Jace has the brain compacity and mouth filter of a two-year-old child! In a just and logical world, Dorothea would have just kicked them out of her apartment and kept the cup for herself. Could you imagine the amount of leverage Dorothea could have against The Clave if she had The Mortal Cup? They would probably do anything to get it back, and if they attacked Dorothea, she would be well protected by the wards on her apartment. And bonus point: If shit gets really bad, Dorothea could just use the portal as quick getaway.
But since Cassandra Clare is a hack, we get none of that!