His wealth was built up bit by bit over many years.
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From Zhu Xi's Song-dynasty 《答周南仲书》: 但使一日之间整顿得三五次,理会得三五事,则日积月累,自然纯熟 - 'if you tidy up three or five times a day and grasp three or five things, then day by day and month by month understanding becomes natural.' Classic Neo-Confucian self-cultivation framing.