My entire childhood I thought it was specific letters for my blocks and, in a way, it is. But for me it’s words or “letters” that I cannot avoid saying. Such as my name. For example the first letter of my name used to be my no-no letter. The first letter of the town I lived in was a no-no letter. You can’t use synonyms for those words. For me, it’s not really specific letters. It’s letters I cannot work around. It just feels like it’s certain letters because they happen often. And the more I think about those unavoidable words, the worse it becomes.