The problem is, you are always right, in your own mind, I have been to court 3 times on a self defense/assault/affray/public disorder question, yes there is an element of who's story convinces the judge in magistrates, and the jury in crown court, but in order to win, you need to convince these people you acted in a reasonable way, and these people have seen it heard it, and been sold it umpteen (thanks Buka) before, they have heard what is plausible in guilty and not guilty people's minds before, they know what is logical and reasonable, if I invade your space, this is not assault, it makes you uncomfortable for sure, but you have to prove or persuade beyond reasonable doubt.
For the record, I won 2 and lost 1, but all 3 occasions, I genuinely believed I was acting in self defense, the 1 I lost was because, I had pushed them to the ground, and followed up with a secondary action, the 1 I lost, the judge told me, had I stopped, after putting them to the ground, he would have took my point, but because I followed up with a secondary action, when at that point they could not have been a threat, I lost, had I waited until they had got to their feet, deemed them still a threat, I would have won.