Ethan Marcotte is an american webdesigner who worked for famous newspapers like "The New York Magazine". In addition, he is the author of some famous articles and books about responsive websites and fluid designs.
To begin with, we should make a link between web design and prepresse. We should think about where we come from and where we are now, and that everything that is shaped on a computer has its origins in something else that we know from the physical world. Think about choosing a canvas, it is the part where we give the work a shape, as an artist you can choose to work on stone or on paper, well in web design the canvas is the web browser.
Long story short, we have to think beyond our own desktop pcs and consider all the different devices that are actually connected to the Internet. To realize the amount of devices that are actually connected to the Internet, we invite you to regroup all of yours on a table.
We should also consider that every project starts with a flexible grid, hence we should work with proportions instead of static pixel sizes to facilitate the process of making things responsive. Another topic is Media Queries, we can consider it as a part of the code that is responsible to resize the text so that it scales better with the images and grid. A brief definition of the Media Queries is: "a CSS3 module allowing content to adapt to the screen resolution".
To conclude, we should keep in mind how the concept of responsive design was created and how nice it is but we should still work on spotting bugs and if needed, work on an alternate design for certain devices.
DAO of flexibility - Crédits - © 2015 Verboogen Benjamin