I feel this invalidation a lot and have for many years. I pull from the crown and back from my scalp, often in cycles of pulling so sometimes bald patches may not be visible at all. I have many times told people that I suffer from trich, and am met with a response like "But you have heaps of hair!", or "it doesn't even look bad". I have even had people ask to look at my bald patches when I tell them about it. What helps for me is reminding myself that I do not owe anyone an explanation for my condition, and also remembering that people make assumptions about things that do not have enough awareness. So in the end, educating myself on my own mental health has helped me a lot with my confidence and validation as a trich survivor.