It’s hardly the case that such a phrase will help a person that came to you for advice or just came to you to get something off his or chest (in such a case, hugs are a much more effective remedy).
“Everything will be okay” marks some kind of undefined point, an incomprehensible theory, according to which it’s not clear what, when and under what circumstances everything will become “okay,”, and how “okay” should be measured in the first place.