During The Day of the Doctor, the Eleventh Doctor wants some dust to be examined. When he's asked if the dust is important, he states that in all his adventures, he has never seen something that wasn't. As it turns out, the dust just so happened to be the remnants of the statues that the Zygons were pretending to be. The Doctor feels that everyone in the universe has an importance and, as he has taken to keeping the Earth safe, he definitely feels every single person on the planet is important to him. Earth is his adoptive home - until Gallifrey is finally found, at least - and the residents of the planet have become like his extended family. Lesson Learned: Anything can be important to a given situation. Don't look past something that seems innoculous.