Một nửa ổ bánh mì vẫn là bánh mì, nhưng một nửa sự thật không còn là sự thật nữa.

Half a loaf of bread is still bread, but a half truth is no longer a truth.

This is describing lying by omission. This is equivalent to “Economical with the truth” (i.e., withholding information) and American statesman Benjamin Franklin’s saying “Half the truth is often a great lie.”