Impracticability is the fact that a plan cannot really be carried out — not because the idea is silly in the mind, but because the real world gets in the way. There is not enough time, money, space, or people; the road is too narrow; the machine is too heavy to lift. You will see this long noun in careful writing: the impracticability of the scheme. In speech, most people just say it won’t work or there’s no way to do it. Though actually, English also has impracticality, and they are not quite twins. Impracticability asks “can we even do this?” Impracticality is more “is this a sensible way to live or work?” Students mix them, and even some native speakers do.

不可行、行不通（不是「不切實際」）