My key turning point in the writing exercises was when I observed this voice in my head telling me "Oh, you don't have to write that down, I'm sure it's not really important." Or "that's a little embarrassing let's just skip it, it won't matter. If I came across any idea or thought that made me feel slightly uncomfortable, that inner voice was more than happy to let me off the hook and tell me it wasn't necessary to put it on the paper.
We all have that inner voice, and it is NOT your friend when it comes to doing this work. I didn't even have any significant trauma in my life history at the time I was doing the SEP (at age 60!) and yet it was reeeally hard to force myself to write down the things that made me uncomfortable! Doing it brought me relief, interesting revelation, and more freedom to keep facing the negative emotions that we continue to compile just by living our lives.
I also know all about growing up in a house where, even though we had a terrific upbringing and a lot of love as well as freedom, expressing emotions was not encouraged, because of course my parents were not people who were raised to express emotions. Having known three of my grandparents - again, good people and good parents, in hindsight I see it in them as well.
Remember that when you journal, you can dispose of what you write, and in fact two TMS practitioners and authors recommend doing so. I prefer the term "writing shit down" to remind myself to just scribble it out onto the paper with complete disregard for readability, and especially to adhere to the first rule of emotional journaling, which is No Editing!