The root of suffering is vividly depicted in a famous Zen parable of two arrows. When you are hit by an arrow, you feel pain, which is physical and isn't always avoidable - the first arrow. Then when you start to think unconsciously about this pain, you start to experience suffering, which is mental and always avoidable - the second arrow.
Recently I witnessed a living example of how this second arrow works in real time. After I sent one announcement about one decision of mine to several people, half of them responded to it constructively, while one of the rest reacted to it emotionally and even stopped saying hello to me though I emphasized that there is nothing personal against them. It was painful to see how he was causing himself suffering by shooting the second arrow to himself.
Unlike in the above mentioned Zen parable, the first arrow didn't exist in this case. He simply invented the second arrow out of nothing by unconsciously giving a negative interpretation to my announcement.
This has reminded me how I myself used to invent the second arrow out of nothing in the same way, thus causing myself enormous suffering. Thank God, I can consciously avoid this suffering in most cases now, and even in what few cases in which find myself about to shoot the second arrow, I can prevent it before it's shot to myself.
This example has also made me realize anew that it's precisely those who are intelligent that are more prone to this second arrow as they are more likely to overthink, and unconsciously at that.
Unless you are specially trained through the practice of mindfulness (meditation) etc. and/or were born with a special talent, most of the thoughts you have are automatic. So thinking for you is more like digesting than like, let's say, reading.
As someone who spent his entire life in his mind-made prison until waking up I've been claiming that meditation should be an obligatory school subject. We are encouraged to think independently at school, but unless we are also taught how to observe out thoughts mindfully, this is extremely dangerous like learning to ride a bicycle without learning how to use a brake. Unfortunately, this is the rule rather than an exception for so many people.
I want to and can help them, but there is one fundamental problem for which I haven't found any practical solution. The problem is that most of these people seem to be unaware of this problem of theirs - the problem that they think on autopilot.
I know this meta-problem very well as I was just like that until the suffering I caused to myself became unbearable and eventually led to my sudden awakening. I don't want anyone else to experience such unbearable suffering, but this might be the only viable solution, at least for some of those who are deeply trapped in their mind-made prison as I used to.