In the game when you get the Institute and the first Brotherhood of Steel quests, it's necessary to go to the brotherhood of steel before you go to the institute.

"Call to arms" quest fails if you don't.

If you go to the Institute and meet shaun first then you'll fail the Brotherhood of Steel quest line and you won't be able to complete the game. Just wasted 4 hours trying to figure out what was going on in the game, not happy at all. This is the worst bug/glitch i've ever encountered in a game.