Assumptions are a dangerous thing, and a little bit of knowledge is even more so, and you would be amazed at the number of people who place themselves at great risk either failing to appreciate the magnitude of the risk that they are exposing themselves to. Worse yet, some people are well aware of the risks, and yet actively choose to reject them outright.
A clear example of this is with novelty contact lenses which are commonly used during Halloween as whilst people casually use them with nary a second thought (probably too busy planning their outfit) there is a number of potential problems associated with novelty contact lenses. In particular, special care should be taken with black contact lenses, as these operate in much the same way as a pair of sunglasses. No doubt there will be more than a few readers who will be somewhat bemused at this remark, so perhaps a more technical definition is in order to clarify the situation.
These particular form of contact lenses have this effect because they are dark and therefore block the passage of light into the eye, by refracting it away. What this means in real terms then is that your vision is clouded which means that you will have to be especially careful in order to avoid sustaining an injury. This is true even if you are in a room where there is a lot of light.
Please note that with black contact lenses (and indeed all forms of contacts, medicinal and novelty alike) that you take proper precautions to clean them before and after use. The last thing you want (or indeed need) is to come down with a rather painful eye infection because you were tardy and negligent in cleaning your lenses properly.