It looks like you are a first-time cruiser (which I have to say is unusual because your name seems very familiar but it must be a coincidence).
In any case - people do not fall off of ships - that is a complete fallacy brought on by trial lawyers who want Congress to make it easier to sue cruise lines whenever someone goes "missing" on a cruise ship.
The sad truth is that suicide by cruise ship happens - just as it happens with the Golden gate and Grand Canyon. I can guarantee you no one has ever accidentally fallen off of a cruise ship unless they were doing something they shouldn't be doing, like going out beyond the safety railings.
When people commit suicide by cruise ship they generally do not leave notes, which makes it possible for lawyers or industry bashers to say it was a crime or accident and then they can sue the cruise line for "contributive negligence." However, so far few lawyers have been successful in proving this in court. Some cases have been settled, however.
There are a few cases that remain mysteries, but compared to the number of people who cruise each year cruising is still an extremely safe vacation option.
Modern cruise ships all have surveillance video cameras that show in most cases overboards did not involve a struggle or another person. In fact - there are no proven cases of people falling or being thrown off of ships except rare cases where the person put themselves beyond the safety barriers.