There is an apocryphal story hereabouts (recalled from memory) about Wittgenstein when he was working as a laboratory assistant in the Royal Victoria Infirmary, Newcastle upon Tyne during the second world war (lodging in the Jesmond house - illustrated above - that is currently, inhabited by some family friends).
Apparently he turned up - unannounced, and at first unidentified - at a philosophy department, seminar presumably after his work had finished: I like to imagine he was still wearing his white lab coat. He sat, stony-faced, through the fumbling talk, as the whisper went around that he was present. When it came to the question time, nobody said anything - waiting for W to speak.
Wittgenstein is supposed to have delivered the following crushing line: "Well, that was very interesting... Now! Shall we do some philosophy?"... And then he, of course, proceeded to take-over the proceedings.
If there is any truth in this, W was being typically arrogant and cruel; but there is a "moral": he did have a point - In the sense that there are few things more boring and futile than studying and expounding "about" philosophy (as happens in 99-point-something percent of seminars); yet (for those with the taste for the activity) there is little in life more fascinating than actually doing philosophy.
In other words; I think Wittgenstein may have been making the point that there is a world of difference between talking-about and doing.
Actually doing philosophy - by oneself or with a few other people - is (like many of the best things) something that can only be done from a genuine motivation; from genuinely wanting to know oneself and for personal reasons.
Wittgenstein himself tried to do philosophy in a formal academic setting, in his "lectures" - but, while he sometimes found an audience of suitable stooges who stimulated him in the ways he required; I don't think he truly succeeded for other people.
Because W's motivations were not their motivations; and his disciples turned-out every bit as conventionally academic and externally-driven as the adherents of any other "school".
So perhaps, like all creative work, real philosophy is essentially a solitary activity.
Note: The "insane" of the title may seem obscure. What I was getting at was that is that when some person, usually an individual, is doing philosophy - he is doing so for personal reasons, that may not be at all widely shared. His work is quite likely to seem incomprehensible, even crazy - especially when seriously pursued, and over a significant timespan. To other people; he seem to be engaged in a trivial pursuit, using idiosyncratic methods, in a thought-world of his own. Insane!...