A friend in need is a friend indeed.

患难见真情。in need并非只有“处于贫困”一种意思。英语很灵活的,in need还有“处于困境”,“需要帮助”等这方面很多意思。这句话的意思是约定俗成的,这里in need要表达的原意估计是A friend comes up when you are in need is a friend indeed。