Summary: Travelling with the Doctor can be hazardous.
If there was a downside to travelling with the Doctor, it was his cavalier disregard for his own and his companions’ safety. He had a bad habit of plunging headlong into dangerous situations without a second thought, dragging whoever happened to be travelling with him along in his wake.
It made for an exciting life, that was beyond doubt, but unlike a Time Lord, humans couldn’t simply regenerate a new body if theirs got damaged beyond repair.
It wasn’t that the Doctor didn’t care about his companions, Martha was sure of that, he just got caught up in the moment.