Things are not that simple. Many times I have encountered that people do not know that they know something, lack of confidence can undermine their abilities. By default they will say their perceived version of "truth" that they "do not know it" while in fact they do. In eyes of their boss lack of confidence can be perceived as reason for demotion or endless cycle of easy tasks that do not lead person to improve their skills and learn by doing. Fear of judgment can be parasailing.
Also, sometimes pressure forces person to learn something in a very short period. So, if you "fake it", but also put significant effort to quickly learn what is needed to succeed then it is not lie but a 'future promise' it would be lie only if you don't succeed.
Also, sometimes pressure forces person to learn something in a very short period. So, if you "fake it", but also put significant effort to quickly learn what is needed to succeed then it is not lie but a 'future promise' it would be lie only if you don't succeed.