Your thoughts create reality or in other words what you hold in mind it manifests. Through Mindfulness you can become aware when your thoughts arise.
Therefore you can choose to change where to focuss your attention. When you bring awareness, you will be able to observe your thoughts, acknowledge them and let them go until they dissolve.
You can choose to create your own hell or heaven, but you’d rather don’t believe what I say, you can only understand it through experience.