两层皮

Traditional (Taiwan): 兩層皮

liǎngcéngpí ㄌㄧㄤˇ ㄘㄥˊ ㄆㄧˊ

    • two things that should be unified but remain separate
    • a disconnect (e.g. between theory and practice)

Character by character

Saying俗语俗語

Idiom惯用语 · Widely known

Literally
two layers of skin
Meaning
A variant of 两张皮: two things that should be unified but remain separate and don't fit together, such as theory and practice.

Sources