"lack insight" is a correct and usable phrase in written English.
You can use it when you want to refer to a deficit of knowledge, understanding, or perception. For example, "The judge's decision clearly lacks insight into the complexity of the situation."
People rarely lack insight in an absolute sense.
Two unauthorised biographies sometimes lack insight but are entertaining reads 1.
There are too many images that lack insight and suggest a first-time-in-the-big-city perspective.
They lack insight into the bitter power struggles, the daily indignities and the subtle sabotage that plague the lives of doctors, especially trainees.
It's a common issue around the globe: many water utilities lack insight into their aging, leaking, inefficient infrastructure, and are employing unimaginative stopgaps or privatizing their operations.
They maintain that one of the reasons so many patients lack "insight" is that they are asked to accept a model of illness that doesn't resonate with their own experiences.
Jointly considering random user distribution and Rayleigh fading, exact distributions of these extreme values become complex and lack insights.
Too many of those involved "lacked insight", it claims.
Throughout Linda's stay at New Hampshire Hospital, her doctors routinely noted that she lacked "insight," a term that has a troubled legacy in psychiatry.
He was not, however, insincere, lacking insight, or, as had been apparent to me since that afternoon in the Circular Congregation Church, easily forgettable.
She often lacks insight — but this is because she has the sensitivity of a tuning fork, and she's hardened herself against too much sensation.
