The unknown attacker may choose you at random, based on his urge at the moment, or he might have noticed you previously and stalked you before making his move. The familiar attacker has chosen you as the object of his rage. His sights are set squarely on you.
The unknown attacker usually acts on impulse. It’s hard, as a rationally thinking person, to understand how someone can act heinously on impulse, but these people aren’t wired like you and I. They walk around with ill intent.
The familiar attacker will usually have a plan to hurt you, specifically. If he snaps, seemingly at random, it is because he has been harboring feelings of anger and rage towards you. Thus, he could have a calculated plan to hurt you or he may suddenly hurt you because his rage against you has reached a breaking point.
Defense against a random attacker can range from verbal resistance to extreme physical force to free yourself from the danger of the attack. Defense against a familiar attacker usually requires an elevated use of force to escape the attack. He will be more aggressive because he knows you and you know him. You can identify him, so the risk for him is high. This means he is completely comfortable with his decision to show aggression towards you—regardless of the consequences.
Although the familiar attacker is more dangerous, the plus side is that you know him, too. You know his name, his face, and his personal information. You probably have a photo you could show to the police.
If you believe someone may be planning to hurt you, take action before the situation occurs. Remember there are always clues. If someone verbalizes anger towards you or has made threats, notify authorities, family, and friends. Do not minimize his threats as just hurt and anger. It could be just that but you don’t want to risk being hurt, so write everything down—the date, a summary of the incident, and who else was around when it happened. It is always better to be safe than sorry.
If someone threatens you, there are no hard and fast rules to define the danger you’re in, due to the random nature behind the motivation of each attacker. The difference between one person and another, convicted of very similar crimes, can be dramatically different.
Thus, you need to have your plan of action ready. You must develop the awareness, confidence, and bravery you need. This takes practice.
I encourage you to take a self-defense class and always pay attention to your surroundings. Leave a situation if someone is making you feel uncomfortable. Attackers don’t want to get caught—therefore strong verbal resistance or screaming can (in some instances) work to repel an aggressor.
Separate yourself from toxic or violent people. Know your exits at all times. Know what to do when it matters most.