This is not necessarily true.
Scientists always say Earth is a typical planet around a typical star in a typical arm of a typical galaxy in a typical galactic cluster, etc.
And while that may be true, everything in the universe is unique. Life (specifically intelligent, sentient life) requires a specific set of conditions to evolve, and while there may be different possible sets of conditions (e.g. not necessarily carbon-based, maybe non-corporeal), it isn't a prerequisite that those sets of conditions have been present for a sufficient amount of time at any other place in the universe except Earth.
I know that may seem mind boggling, but it's no more mind boggling than trying to grasp the size of the universe.