На чужую одежду плохая надежда

It is not reliable to count on someone's goods Cf.:

Borrowed clothes (garments) never fit (Am.). Borrowed garments fit not (never fit well) (Br.). Не goes long barefoot that waits for dead men's shoes (Br.). Не that waits for a dead man's shoes may long go barefoot (Am.). Не that waits for dead men's shoes may go a long time barefoot (Am.). You can't get warm on another's fur coat (Am.)