What is the reason why the leaves of a gentleman's orchid turn yellow?

First, the basin soil is too wet or too dry, which causes root rot, root dryness, weakening of root absorption function, and insufficient supply of water and nutrients, resulting in the yellowing of orchid leaves; the second is the direct light in summer; the third is the harm of diseases and insect pests; the fourth is to change leaves, that is, when orchids sprout in spring and autumn every year, there will always be a batch of orchids.

The orchid leaves of three-and four-year-old plants are yellow, dead and shedding, which is a normal metabolism.