As you focus your mind on a particular subject, you start to flow energy towards it. The purer your thoughts are upon a topic, the more powerful the energy flow and the more powerful is the resulting thought form that is created.

This thought form vibrates at a certain frequency and as you focus on it more and more, you start to gain vibrational access to other information on a similar vibrational frequency to that thought form. It is similar to how a tuning fork at a certain note causes other tuning forks of that note to start to vibrate too even though they might not be connected in any physical way.

This information flow between thinker and subject is what you could call insight.

So, to sum up, focus your mind clearly on a subject that you wish to gain insight about - the early lessons of The Master Key System are all about enabling you to concentrate your mind in this non-resistant, relaxed fashion.

Sooner or later, the insights that are coming to you while in this state will reach a point where the solution to your problem will become clear, or the next step in your endeavor will become obvious.

I believe this is what is intended by the term sufficient insight - and I think that the exercise that is being given is an exercise in being able to concentrate clearly enough (in the way I've mentioned above) on gaining insight into the fact that knowledge without an accompanying application of focused thought (the ability to think) is of little value.

I hope this is clear.