From a design or research perspective there is no such thing as ‘nature’, ‘natural’, or ‘common sense’. Natural should be taken in both senses of the word – the ‘unspoilt’ or ‘non-man-made’ part of the world and natural as in obvious. Nature or the natural world is a relative concept conditioned by cultural preferences. For example, landscapes were not always seen as something with aesthetic value which explains the absence of landscape painting as a legitimate art form before the 18th century (in western culture).* Therefore, there is always some cultural viewpoint at work when speaking about nature or referring to something as natural.
When someone says ‘it goes without saying’ you need to ask why it should not be said (or questioned). This often refers to the idea of common sense which is considered instinctual, eternal or natural (second nature). As with nature ‘common sense’ changes and evolves and has no absolute or fixed state.
The point here is that you should question those things that seem second nature, obvious, traditional and common sensical, not because obvious and traditional things are bad but because there is always some cultural basis behind it. In the most extreme cases common sense is used to hide uncomfortable questions or conditions. In other cases it may simply stand in the way of better, more progressive or sustainable solutions.
*Picturesque landscapes are often though to be patches of preserved and unspoilt land but are in fact artificial and composed clusters of trees, lakes, rivers and hills. The lakes and hills in Prior Park, Bath, for example, are all man made. This image of nature subsequently coloured what we think a natural landscape should look like. Another example is the present and protected form of the South Downs in Southern England which have aquired their look due to centuries of sheep farming. This image is now protected as a ‘natural’ landscape.
Source: The idea of questioning ‘common sense’ comes from Roland Barthes who often questioned everday ideas or habits only to find rich cultural and historical origins behind them.
South Downs National Park