The only man who behaves sensibly is my tailor; he takes my measure anew every time he sees me, whilst all the rest go on with their old measurements, and expect them to fit me.

Shaw contrasts the tailor’s practical habit of re-measuring with society’s tendency to freeze people in outdated assumptions. The “measure” is both literal (a body changes) and metaphorical (a person’s views, character, and circumstances evolve). By praising the tailor as the only one who “behaves sensibly,” Shaw satirizes friends, critics, and institutions that keep using old categories—treating someone as they were, not as they are. The remark also reflects Shaw’s broader interest in social perception and the mismatch between lived reality and conventional judgments: genuine understanding requires continual, attentive recalibration rather than reliance on inherited impressions.