The TARDIS doesn't pick just anyone. It picks whoever's already a little too big for the life they're currently living.
Rose would say yes without fully thinking it through, curious and warm enough that the risk barely registers before she's already stepped inside. Clara would arrive with her own secrets already in motion, clever enough to keep pace with something that's supposed to be impossible to keep up with. Donna would show up loud and unimpressed, refusing to be dazzled by anything before she's decided it's actually earned her respect. Amy would run toward the danger before anyone finished explaining it, fierce and a little reckless in exactly the way the universe keeps rewarding.
Fifteen questions to find out who'd actually step through those doors.
