There are a few council elections that have been based on a coin toss, but that's hardly a big issue. I only said "rarely" because it's literally not "never". I have never made the point that your one vote is "the one".
You appear to be taking a general point about all our single votes adding up to make a difference, and suggesting it's all about you. It's not. Plenty of people have made the same point to you - it's the individuals that collectively make a difference. I don't care how *you* vote, but I do care if your attitude that it makes no difference is one that more and more people hold.
The "no other valid reasons" makes no sense.
I was only making one argument - I disagreed with your point that a single vote makes no difference. If you want to pedantically claim that one specific person doesn't change elections, then you're right, but it's not about one specific person, it's about everyone who believes that, in your words "the outcome will be the same as if they had never left the house."
Clearly that's not true, as we know that people voting does make a difference to the outcome.