At Flordyce University any student who wants to participate in a certain archaeological dig is eligible to do so but only if the student has taken at least one archaeology course and has shown an interest in the field  Many students who have shown an interest in archaeology never take even one archaeology course
Ttherefore, many students who want to participate in the dig will be ineligible to do so
An expensive new building will prove to be a good investment only if it is aesthetically pleasing or provides lots of office space. However, since many expensive new buildings are not aesthetically pleasing, few expensive new buildings will prove to be good investments.