That's an excellent question, Clifford.
This is an issue that was bothering all of the global community of container carriers, and also the safety of the container vessels.
I believe it was about six or seven years ago when IMO implemented the mandatory weighing of all containers. You will know that the container vessels are generally top heavy, so that also creates some stability issues. To ensure the stability and the safety of the vessel and the crew, it was important that all the containers be weighed before loading. All of that is included in the plan and has been verified ashore. Also, after loading, the master has to verify that the vessel is safe for a voyage.