We suffer when the mind story that we live only within our psyche deviates from reality.
Pain, both physical and mental, simply happens beyond our will. The body gets sick, we get injured, a dear friend dies. We cannot do anything about it. Suffering is very different thing and only when one is lying between the coils of ignorance it gets mistaken for pain: suffering does not happen; one chooses to suffer, mostly unconsciously.
What is it that creates suffering? The mechanism is so simple that if understood it would ease the situation a lot. We suffer when the mind story that we live only within our psyche deviates from reality. Living the present means that you will not experience suffering.
Some examples: you're in love and she/he leaves you. The mind tries to react to the pain caused by loss by producing mental images that seem to alleviate it while instead they create suffering. You start living the mind story in which you are with her and the fact that she is not there makes you suffer.
Another example: you are in bed with the flu. If you simply live in the present and enjoy the flu it’s all good. Yet, if you start picturing a movie where you imagine others outside, having fun and you could be with them, you suffer. And again: you live in a difficult place, maybe shredded by war and your mind starts to create an alternative reality. The first part is pain, the second is the mind reaction that creates suffering.
I could show you endless examples but I think the mechanism is clear. If there is pain and it is possible to do something about it, then it is right to act upon it, if you start to enter a mind story you may initially feel a sense of relief but in doing so you open the door to suffering. The more you suffer and give up, the less you have energy to act and eradicate, when possible, the pain. Having these mechanisms clear and taking a close look at yourseld when they are in place would be the starting point to have a better life and that one would choose to suffer it’s personally something I find shocking.