Ever heard the saying: “You only know what you had, when you lost it.” This is the whole backbone for negative visualization. Negative visualization is the act of picturing something in your mind that will make you feel bad. When you finish with the visualization, then you can return to the life where you have it better.
What makes you truly happy?
Are you chasing happiness? Did you find it to let it slip away from you again? Isn’t it weird how it always happens…medium.com

A more concrete example is about the end of the life of your kids or parents. Many people have the feeling that they should have done more with those people. However, by then it is too late, and they have died. The grieving will be more intense if you feel like you wasted the opportunity to be with them.

Make it worse to have it better

Negative visualization would have you imagine them dead maybe by a car crash, or by sickness. It doesn’t matter how they died, as long as they vanish from your mind. Your mind will grieve, you will feel the pain. Then you stop with the visualization and return to the real world where they are alive. You now witnessed how you will feel when they would not be in your life. Act on those feelings. Spend more time with your loved ones.

It’s all about knowing what you can lose and how it will make you feel. Before it happens.

It is also possible to visualize a situation that is even worse than the current situation. For example, you broke an arm, and you have problems going through your daily life. Visualize that you have broken both your arms or maybe a leg. Imagine you have even more troubles. Imagine you have to deal all that by yourself. Suffering through all that and feeling miserable. When you have finished your visualization, you will feel happy about your current situation. It can be much worse. Your current situation isn’t that bad after all.

It’s all about having that point of reference. Make your current situation look better in comparison to what you can visualize.