1) Have an SUV with a carpeted cargo area in the back
2) Transport a Christmas tree inside said SUV
3) Don’t clean it for the next three months
Then don’t be surprised when
4) On the first nice day of spring you spend over two hours trying to vacuum out all the little needles. Because during those three months the needles have formed a close personal relationship with the carpet fibers, attempted to breed with them, and when that failed, burrowed in deeply to die. And now the carpet fibers are holding on to the dead needles for dear life, because apparently they are not done mourning yet, and thus cannot be bother to give a flying fuck about minor details like needing to get the car clean before we start trying to sell it.
Moral of the story:
5) Get an artificial Christmas tree.