Filling Up A Grid - 3 * 3

If we look at the square: we can see that there is a square in the middle, which borders all of the adjacent squares, therefore if we were to put any integer $n$ from $1$ to $9$ , there is an $n$ - $1$ and/or an $n$ + $1$ which must also be included in one of the boxes surrounding the middle box, and if the middle box touches all of the boxes surrounding it, it must touch the number(s) that lie consecutive to it.

The central square shares either a side or a corner with all the surrounding squares, so no number can be put there.