A good designer always tries to see things from the point of view of the user (or the customer, viewer, audience member, etc.). This is the ol' "It's not about you it's about them," a precept which is applicable to most aspects of business (or teaching, etc.). When we think about design, it's usually when we encounter poor design: an ambiguous sign, a confusing website, or text on an information board that is too small to read, and so on. This is why I always say to professionals aiming to become more design-mindful that they must learn to slow down and take note of the good and bad design that they encounter every day. Take a picture, write it down, keep a scrap book, pay attention. Lessons are everywhere (and free). Here's one that I noticed in my sports club the other day in Osaka that touches on the issue of putting yourself in the users' shoes and the general graphic design principle of contrast.
The picture below was taken with my iPhone and is a good representation of just how I saw the numbers (in lbs and kilos) printed in white on the stack of black plates on the lat-pull machine. The size and color of the sans serif type had enough contrast with the black background of weights to be read without difficulty. From even a small distance type can begin to appear fuzzy, but the sturdy sans serif typeface was perfectly clear. De-emphasizing the lbs. and kg unit marks also helped with clarity (yet, are the lbs. & kg marks really needed after the first row?).
Below is part of a leg-press machine. This picture is a perfect representation of how I saw the numbers on the weights when I turned my heard to the left and looked down to adjust the weights. I could not read any of the numbers on the slabs of iron. Not a single one. The plates were of similar size to the previous machine, yet why was I unable to read any of the numbers (my vision is nearly perfect with lenses)? Let's bend down for a closer look.
(Below) When I leaned down as far as I could and stuck my face just a few centimeters from the stack, this is what I saw. With difficulty I could make out the top 5-6 rows only. Did the person who approved the labeling of the plates ever actually use the machine as intended? On an assembly line or on a computer screen the labels may have seemed legible, but what about the real world context? This is a very small thing, but it matters (it can be dangerous to attempt to lift a weight that is too heavy, for example).
There are many ways to improve the legibility of the labels on this machine. First, you have to ask if lbs. is even necessary. In Japan, like most parts of the world, we use the metric system. Most of the users here will read the kg number (yet it's in a subordinate position). If both measurement units are necessary, then use greater spacing (for example) to separate the numbers similar to the first example at the top of the page. Other things that make the type harder to see include the smaller size, the thick line, and the fact that the type is oblique. Having the unit marks the same size and weight does not help either. It all just blurs together.
Another reason for the poor legibility of the labels has to do with reverse type. Typically, reverse type is a light typeface on a dark background. For example, white on black, where the background element (such as a box) prints and the text is knocked out so that it doesn't print, letting the white paper show through. In the example above, because the background black "canvas" of the plates is the same color as the type on the white labels, it has a similar effect to reverse type. We see a lot of white, but we can not see the knocked out part or the emptiness which forms the shape of the numbers and letters clearly. In the example above, placing white type on the black plates would have made for far greater clarity.
Reverse type can be effective if used with restraint. Whether it's on a page or a slide or a poster, reverse type is going to stick out and attract the eye, which is why you use it sparingly. If you use loads of reverse type on a single design, it may just amount to a lot of noise. Below are a couple of slides. Notice how your eye was clearly drawn to that large black dot (in fact, it was likely the first thing you noticed when you scrolled down this page).