"In 1952... I tried to explain the behavior of the new "strange particles," so called because they were copiously produced as though strongly interacting and yet decayed slowly as though weakly interacting. (Here "slowly" means a half-life of something like a ten billionth of a second... a strongly interacting particle means... a ten trillionth of a second, roughly the time it takes for light to cross such a particle.) ...I thought of assigning these strange particles isotopic spin I = 5/2... But the notion failed to work... I was invited to talk at the Institute for Advanced Study... By a slip of the tongue I said "I = 1" instead... Immediately I stopped dead, realizing I = 1 would do the job. ...But what about the alleged rule that ic strongly interacting particle states had to have values of I like 1/2 or 3/2 or 5/2? ...the rule was merely a superstition... unnecessary baggage that had come along with the useful concept of isotopic spin... [which now] could have wider applications than before. ...[T]he strange particle states differ from more familiar ones such as neutron or proton or s by having at least one s or "strange" quark in place of a u or d quark. Only the weak interaction can convert one flavor of quark into another, and that process happens slowly."