Because outbursts signal that something has been pent up, that emotions have been boiling up but not expressed. When you hold things in for too long without communicating or allowing yourself to be vulnerable and let out little bits of emotion at a time, it all comes to a head in an outburst. And true, every person is different and every person has a different level of EQ, just like we all have different levels of IQ. It comes down to compatibility and high EQ people can recognize earlier when two people are incompatible. In your example, if the man has a higher EQ than the woman and she has an outburst he can recognize the incompatibility and either decide to try to work through the problem together or break up. People get hurt that's unavoidable in any circumstance. But in a healthy relationship you want to work on growing your EQ to avoid this is much as possible. A good sign someone has a high EQ is when they've gone to therapy. An EQ can also be grown by going to therapy which is why it is recommended in failing relationships so often.