You are not actually worried about the email, or the symptom, or the decision. Not underneath. Underneath, you are trying to escape a feeling: the discomfort of not knowing for sure. That is the engine, and once you see it, a lot of separate worries turn out to be the same problem wearing different clothes.
What intolerance of uncertainty means
Intolerance of uncertainty is exactly what it sounds like: finding not-knowing genuinely, physically hard to bear, and doing almost anything to make it stop. Researchers have built a whole model of chronic worry around it. Work on the intolerance of uncertainty model of generalised anxiety places this trait at the center of how excessive worry develops and keeps itself going. The unbearable thing is not really the bad outcome. It is the open question.
Why thinking cannot fix it
Here is the cruel design flaw. The mind reaches for certainty using the only tool it has, which is thinking, because thinking at least feels like doing something about the unknown. But certainty is not actually on offer. You cannot know for sure how the meeting will go, or what your friend meant, or whether you made the right call. So the mind keeps grasping at a fruit that is not there, and calls the grasping thoughtfulness. This is why answering one worry just spawns another. You were never going to reach the bottom, because the demand was for a guarantee, and guarantees do not exist.
That reframe is genuinely freeing. The problem was never any particular worry. The problem is the underlying demand for certainty itself. Which means the path out is not to think harder until you finally know. It is to slowly build your capacity to not know and be okay anyway.
Building the tolerance
You raise tolerance for uncertainty the way you build any capacity: with small, repeated reps. Every time a what-if arrives and you decline to chase it, saying something like, I cannot know this, and I am willing to not know it, you are doing one rep. It feels wrong at first, almost negligent, because the anxious mind insists that worrying is a form of preparation. It is not. We go deeper into the practice in how to build tolerance for uncertainty.
It also helps to sort your worries first. Some are solvable, and those deserve a plan and an action. Others are pure hypotheticals with nothing to do right now, and those only respond to letting go. Confusing the two is a classic trap, which we untangle in the solvable versus unsolvable worry test.
A note on the everyday version and the clinical version
Struggling with uncertainty is normal and human. But when the worry becomes constant, spreads across most areas of life, and feels impossible to control for months on end, that can be a feature of an anxiety disorder rather than a habit, and it is worth talking to a professional. The NHS guide to generalised anxiety describes that persistent, hard-to-control pattern and the support available for it. Reaching for help there is a sign of good judgment, not weakness.
A small experiment
Try this the next time a what-if grabs you. Instead of trying to answer it, name it out loud in your head: this is my mind reaching for certainty it cannot have. Then, deliberately, leave the question unanswered and turn your attention to the next real thing in front of you, a task, a conversation, the walk to the kitchen. Notice what happens. The discomfort of not knowing rises, peaks, and then, if you do not feed it, starts to fall on its own. Anxiety is a wave, not a permanent state. Every time you ride one out without resolving the question, you teach your nervous system that uncertainty is uncomfortable but survivable, and the next wave is a little smaller.
This is the opposite of what the anxious mind wants to do, which is to grab the question and wrestle it until it feels certain. The wrestling is what keeps the wave high. Sitting with the open question, awkward as it feels, is what lets it pass. Do this enough times and you are not just handling individual worries. You are lowering the baseline that produces them.
For most everyday overthinking, though, the move is the same: stop trying to win the argument with uncertainty and start building your ability to live alongside it. That single shift quietly drains a huge amount of the noise. We build the whole practice around it in The Overthinker's Manual.