The screws all break if the sheer force is sufficient. Nails bend.
Or pull out. Bigger screws, or more screws so the fastner tensile (or shear) failure force is more than the the force that the wood can apply to the fastner(s).
Brettski had to tighten up the fastners on one of his treated wood projects because of wood shrinkage. If the wood shrinks away from the nail shank, the holding power is gone. Personally, I prefer screws, but ringshanks are a close second.
