Full Idea
Starting from set theory as it is historically given ...we must, on the one hand, restrict these principles sufficiently to exclude as contradiction and, on the other, take them sufficiently wide to retain all that is valuable in this theory.
Gist of Idea
We take set theory as given, and retain everything valuable, while avoiding contradictions
Source
Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908], Intro)
Book Reference
'From Frege to Gödel 1879-1931', ed/tr. Heijenoort,Jean van [Harvard 1967], p.200
A Reaction
Maddy calls this the one-step-back-from-disaster rule of thumb. Zermelo explicitly mentions the 'Russell antinomy' that blocked Frege's approach to sets.