A talented young engineer (named Alex) at a well-respected medical supply company has been asked to subject one of their products (P) to a final series of safety tests before the company submits P to government regulators to inspect before the company puts P on the market. Alex has been given one week to complete these tests and submit a report to the company with the results. Ordinarily, one week would be plenty of time, but Alex is especially busy this week with matters both professional and personal. As such, Alex thinks about asking for the assignment to be given to someone else, but Alex realizes that this action would not look great. Alex is hoping for a promotion in the coming year. Alex accepts the task, and tries to fit in the safety tests when possible. However, by the time the end of the week comes around, Alex still has not finished half of the required tests. Alex considers asking for an extension but decides against doing so (there’s that potential promotion to think about). Alex thinks, “I’ve done some of the tests and P was safe in those. Further, I’ve spoken to people who were involved in earlier series of tests and others who were involved in the construction of P, and they were pretty confident that P is safe as it is. I’m up against a deadline here. Anyway, the government regulators will give P a look before allowing us to sell P, so I’ve got a bit of a safety net. I’m going to pretend that I did the last several tests (by filling in the report with numbers that we could reasonably expect to show up). Then I’ll sign the report, submit it tomorrow, and that will be that.” This is just what Alex does. Luckily, P turns out to be quite safe. It passes the government inspection without issue and goes on the market soon thereafter. Alex even gets the promotion later that year. Why would John Stuart Mill think that Alex almost certainly acted wrongly in this case, even though things seem to have “gone fine”?

In On Liberty, John Stuart Mill wrote that an individual was allowed to do harm to himself or herself but not to others. He believed that government and authority over others should exist only to prevent individuals from doing harm to others. 
While an individual can, he believed, choose to harm himself or herself, a person does not exist in isolation. Therefore, harm done to oneself (in this case, Alex's lie that he completed all the necessary safety tests) can in fact hurt others. Therefore, while the product seems to be safe, it may have defects down the line that have not yet been discovered. Therefore, Alex's decision to lie about having carried out the safety tests may eventually hurt other people. His lie has the capacity to harm others and not just himself. Accordingly, he violates John Stuart Mill's "harm principle."
In addition, Mill considered acts of harm possible from omission, not just commission. In other words, an individual can do harm by not doing something, not just by doing something. If an individual saw a fire and did not report it or try to put it out, for example, he or she would be violating the harm principle. Therefore, even though Alex does not commit a wrong by his actions, his inability to finish the safety tests is an act of omission that violates the harm principle according to John Stuart Mill.