This follows on from the post below...
1. The most solid knowledge - that is, least prone to error, external influence and wishful thinking - is that which comes to us spontaneously, unsought.
In other words, this is the imaginative knowledge that comes-into the mind without mediation either by five senses' information or of reasoning. It 'appears' - it is 'just there' - and we know it by intuition (of course, summarising and explaining imagination are extra, and fallible, processes).
2. By purposive concentration on a theme or question.
This knowledge is more prone to error, wishful thinking etc. What tends to guard against this is when we allow ourselves to 'brood' patiently on matters, without a deadline or sense of urgency.
This patient brooding allows the proper question to become clear, as well as the answer - because asking too-narrow a question is to introduce un-noticed assumptions that may not be correct.
Patient brooding is the proper way to fill gaps in our knowledge, or deal with personally vital questions.
3. Imagination becomes error prone when it is used against a short timeline to answer questions that we are not personally engaged by - when used to answer 'idle curiosity' or externally-originating commissions.
Note: This is where I think Rudolf Steiner went wrong in his later career as a clairvoyant: that is he used his imaginative ability urgently (against a deadline, such as a projected lecture course) to seek detailed answers to questions that were not of primary concern to him; and also questions which came from other people.
Biographers agree that much or most of Steiner's later work (including the vastly detailed historical material, training methods for doing Spiritual Science, work on medicine, agriculture, education etc.) was done in response to an external agenda.
In addition, the vast number of lectures he gave, from 1904 more than 150 increasing to more than 400 lectures per year - I believe led him to 'force' answers using a standardised psychological 'technique'.
Steiner came to believe that answers to anything and everything were to be had, instantly, and for the asking... These were then 'automatically' systematised - quite naturally for him, using his vast intelligence and memory, into the trained 'German Professorial' form in which they were recorded.
This is my explanation as to why the great bulk of Steiner's output is wrong, irrelevant and off-putting - but nonetheless (and especially the early material, but intermittently through his life) he also produced basic and essential insights and knowledge.