Truth Is.

You'll never know how it feels like until you have really gone through it. Thus, my advice is don't simply go around assuring people that you know how it feels like and what nots because you don't. You don't and you won't until you have really gone through it. Fact.

Yes, it is understood that you're just trying to portray your sympathy towards someone. However, there are really so many other ways to sympathise them. Well, it somehow or rather saves your ass too. Cause, trust me, you'll have a very difficult time trying to comfort someone if you don't really know what it actually feels like. Perhaps, a hand over their shoulders or a word of "Don't worry, I'll always be there for you." would be much better and easier than you trying to crap something out and end up hurting them instead.

Think, before you talk or act.
And stop acting as if you know everything.