Heinrich's domino theory - step three
Here we have taken out one domino, (risk), by making sure that the load being carried is secure. The other factors, and there may be many, are still there and the accident may still happen but at least no one is injured or killed.
A forklift operator may go on a brilliant training course but due to various factors, may not be able to operate the truck exactly the way s/he has been taught.
By eliminating as many "dominos" as possible the risk of a serious accident is reduced.