Usually it was because he privately, and often publicly, criticised their results, although one would have to say that Landau was extremely knowledgeable and was almost always mathematically correct:
Karaniwan, ito ay dahil siya ng personal, at madalas sa publiko, criticised kanilang mga resulta, kahit na ang isa ay upang sabihin na Landau ay lubhang matalino at noon ay halos palaging mathematically tama: