I don't know if this is the way things work, it probably isn't, but my opinion is that while yes, everything is possible, things like lifting crates are impractical. I believe telekinesis is possible, yet most of us (including me) haven't developed the abiliity because it is difficult and not useful in the real world. I have two theories on this, which explain the reason we can't lift big objects or better, ourselves. In my opinion we do use our whole brain, so it is not a matter of actually using more brain, but of reteaching it to be able to tap into the energies we have inside us in their purest from. Also, I believe that like light, which is basically pure energy, our energies diminish by the square of the distance, and when passing through dense objects (like us), so what takes your body almost no energy (like lifting a pencil), takes much more energy when it has left your body, as the strength weakens dramatically from the passing through your skin and the distance to the object. This I believe is the reason it helps to have your hands close to the object when doing telekinesis (if you can actually do it, not me). This combined with the fact that no one can fully utilize the energies available to us, even though our body is a big chunk of energy, and that energy weakens strongy when leaving the body (kind of like light passing through a filter), cause us to not be able to do amazing telekinetic acts.

Note: I am not saying anything I am saying is fact, I know no more (very possibly less) than any of you, but this is my belief on the workings of the universe.