I can't believe I missed this thread.
I'm a 2nd Dan black belt in ITF Taekwondo, as well as holding a 1st Dan in Kukkiwon Taekwondo, I also practice Judo and have reached 1st Kyu and am currently building points towards my 1st Dan in that too. I've trained in Taekwondo since I was 5, I had a break from the age of 17 to 21, then took it up again, and I've learnt underneath this instructor for the last 7 years.
Martial arts is great for self defence, because someone who practices it fully will know when to get the hell out of a situation before it becomes violent. Verbal de-escalation should also be taught, talking your way out of a situation in a calm and controlled manner devoid of threats. If it does come to fisticuffs, well as long as you realise that fending off an attack is not the same as sparring then I always find it prudent to remember that the fight usually leaves people after 30 seconds, that's a long time to receive some damage, but if it's truly 1 on 1, then it's not a lot of time to evade attack, space allowing. It's also worth remembering that one good connect will end a fight, that's both you as the defender giving the attack, or receiving it. Sometimes no amount of training will prepare you for that one punch to the gut that they somehow just manage to connect just right.
In terms of actually applying any of this, well the last fight I got into (and only fight as an adult) was three years ago, and after a lot of being pushed around and basically trying to back out, I lashed out at his knee and then used an open palm under his chin and pretty much threw the guy to the floor. He hit a flowerpot on the way down and passed out cold, the police got involved, there were a lot of witnesses to say that I acted in self defence, so I was let off any charges, but for that split second before he came around again I thought I'd killed him (adrenaline does some weird things to your head) and I can honestly say that was the worst point in my entire life. Fortunately, martial arts has also given me some of the highest points too.