Religion
A religion only means something so certainly posed that nothing can ever displace it. It is an attempt to settle first principles so authoritatively that no one need so much as even think of ever re-opening them for himself or feel any, even the faintest, misgiving upon the matter. It is an attempt to get an irrefragably safe investment, and this cannot be got, no matter how low the interest, which in the case of religion is about as low as it can be.
Any religion that cannot be founded on half a sheet of note-paper will be bottom-heavy, and this, in a matter so essentially of sentiment as religion, is as bad as being top-heavy in a material construction. It must of course catch on to reason, but the less it emphasises the fact the better.