I was recently revisiting the ladder technique. But what I gather about that part of the exercise is, to demonstrate the power of your imagination when used in the manner that Neville suggests, (during SATS at bed time).. It shows that despite you spending the entire day thinking and intending the opposite, what you did briefly in imagination during SATS eventually prevails.

A faith building exercise in the Law. You can replace the "I will not climb the ladder" part of the exercise with anything... Fears, doubts, worry, etc that you may experience during the day when you're trying to manifest something. Thats what I gather from it, anyways.