The Doctor either looks for problems or the TARDIS brings him to the problems. When asked, the TARDIS said in "The Doctor's Wife" "I always took you where you needed to go", which suggests that the reason the Doctor so often finds trouble on his journeys is because the TARDIS takes him to it. The Doctor also seems to like the excitement of being in a tricky situation, saying "There's loads of boring stuff like Sundays and Tuesdays and Thursday afternoons. But now and then there are Saturdays. Big temporal tipping points when anything's possible." ("The Impossible Astronaut"), which shows that he wants to seek out trouble for the excitement it brings.