The only difference between a rut and a grave is their dimensions.

Glasgow’s aphorism equates habitual stagnation with a kind of living death. A “rut” suggests repetitive routine, complacency, and the narrowing of possibility; a “grave” is the final narrowing, where change is impossible. By saying the difference is only “their dimensions,” the line compresses the distance between merely going through the motions and being truly alive—implying that a life confined to unexamined habit can resemble death in everything but scale. The remark fits Glasgow’s broader interest in the costs of social conformity and the moral/psychological consequences of settling into fixed roles rather than pursuing growth, risk, or self-renewal.