One of the most important things designers learn with time is to have a sense of proportion. This is one of those principles of design that with time becomes sort of a second nature to you and I might even say some becomes experts at manipulating it.
It refers to the relative size and scale of the various elements in a design. It's a matter of the relationship between the elements of a design composition. It is important to have a sense of proportion because all elements are connected, they should be proportionally related to one another and to the whole.
For example, in the project I'm working on right now I have to install a large chandelier and four around it. The size of the smaller ones have to be proportional to the big one and the big one has to be proportional to the space so it doesn't look overwhelming or too small that it dissapears in the space.
Every single part of our bodies is proportional to the other... our fingers to our hands, then to our arms and then to the whole body. Most designs are done in proportion to our body, the kitchen cabinets are proportionally dimensioned and so is the dining table and the height of the chairs... check it out by yourself and marvel at it!
Have a great Monday!