Certainty

Anyone else has an issue with that? For example when you hear people with OCD even with HOCD saying stuff like, oh yeah this is my obssesion but I know i'ts not true, but it sucks cause for you it feels very real and you even believe it's actually true, that you feel this is the real you, that it's part of you now and this is all you have, and I don't even mean the whole "It feels so real but I know it's not" I mean "It feels so real, and I believe it is, but I don't want it to be, but everything in me it's telling me it's real, my thoughs my emotions my phisical sensations my perception of reality, EVERYTHING"