It occurs to me that RTD was frequently happy to sacrifice character on the altar of Rule XII. Example - Jack Harkness was the most proactive character imaginable until the end of POTW, when he meekly allowed himself to be left behind and entered a new phase of his existence as the Doctor's bitch.

And how much more powerful it would have been if it had been Martha's own idea to walk the earth and build up people's hope to defeat the Master. Instead, she endured all that hardship to carry out the Doctor's orders, only for him to beg the bastard not to die on him.

No wonder she left after that.