the best glues actually alter the molecular structure of the surface they are sticking to, to make it stick to the glue which holds the 2 surfaces together... otherstuff like water or fish based glue (yes, fish) are just "sticky" molecularly and are designed to make a random pattern of molecules from glue to surface so that when it dries it is strong in all "directions" which is why sometimes if you move 2 surfaces as they are starting to stick you end up with an adhesion which is strong if you move one surface up or down, but will let go if moved side to side... the molecule strands have been straightened by the moving-when-not-stuck-properly process!