Each student then presented his symbols to class to test comprehension. Many research studies have recorded similarly low rates of graphic interpretation. One common reason is the cost of compliance. If a warning says not drive for two hours after taking a drug, then the likelihood of compliance is a function of the time and expense required to finding alternate transportation. Other factors lie inside the user.
Some people are risk takers and more willing to risk the consequences.
People frequently ignore swimming pool signs concerning possible dangers. This occurs, at least partly, because most people haven't broken their necks by jumping off of a diving board and don't know anyone who has. Conversely, people who know of bad experiences of failure to comply will be more likely to heed a warning. I only started wearing safety glasses around power tools after meeting someone who had lost an eye from kickback on a table saw. The hazard was no longer an abstract concept.