No. They probably don’t. They may or may not insist they do but unless they already have a TBI of their own, they don’t.
However, annoying as it can be to hear someone say this, they probably do mean well for you. One mistake I was making in the early weeks and months after my crash was telling people, no insisting, that they actually didn’t know how I was feeling. I didn’t realize that I was pushing people away when I’d do that. Heck, I didn’t understand much of anything I was doing, much less remembering any of it unless it was something I texted or typed (Swyped) on my phone. (My eyesight was messed up by the crash and reading was impossible unless I could hold the screen at a certain angle so books and my laptop were on the bench. I was living through my phone. Got pretty good at Swyping though.)
The people who understood the most were the therapists I began working with. More so than the doctors. Yes, the docs would examine me and determine what was needed but it was the therapists spending much more time with me one-on-one that got through to me best. Even though they may not have had a TBI, they at least let me know, patiently, that they were used to clients with my problems and could take whatever I happened to dish out on a given day.
It took me all summer to come to better terms with myself and how my emotions were much more volatile or more relevantly, friable since the accident. And in the early days when I needed people the most I was not helping myself by getting frustrated when people would say they understood how I felt. Unfortunately I do not know how to remedy this for the TBI patient. All I can really do here is add my voice in with the millions of others asking loved ones and friends to not give up on them. I know I didn’t always make it easy for the people around me.