I just explained it in comparison with an attempted murder which would almost certainly have no doubts cast on it. for example, say Lewis was annoying me because he can't read questions, so I decide to kill him by making a bomb. Now I have no knowledge of explosives at all so I make a bomb, which in the eyes of a reasonable person, could not go off or cause any harm. However, the point is that I fully intended and believed that the bomb would go off and if the law said that an crime must be certain in order to be a crime then there would be a situation where it was legal for anyone to attempt murder with no consequences unless the attempt was successful.
Theres a distinction between obscure thoughts and actions and something which has clearly been thought about and attempted with the sole aim of murder.