No shoes but loafers are sold in this store. The shoes sold here can be expensive. All loafers are sold in this store. Some loafers are expensive. No expensive loafers are sold in this store.
Every successful mechanic uses cast-iron wrenches.
Some mechanics use wrenches made of something besides cast iron. So some mechanics are not successful. All valid syllogisms are incapable of surprising you. Some syllogisms are not at all able to surprise you. So some syllogisms are not valid.