Van Der Waal's adhesion.

siddharth5129

I have researched a little online and apparently Van Der Waal's adhesion forces play a key role in the sticky properties of glue and the bonding between gecko setae and tree surfaces. What I don't understand is why this adhesion doesn't happen between the surfaces of any two solids brought in contact. Even if this does happen to some imperceptible extent , why aren't the surface-surface adhesive forces as strong as the cohesive forces between the molecules of each solid, which should render them very hard to separate.(the surfaces should be broken apart to separate them)