Ren (forebearance-tolerance) is the key to improve one's heart / mind nature (Xinxing). To endure with hartred, grievance or tears is the Ren if an ordinary person who is attached to his misgivings. To bear with any hatred or grievances at all is the Ren of a practitioner (spiritual aspirant).
Source: Essentials for Further Advances
Contributed by: Bhiish'ma