Not a hard rule at all. What I meant, is that I don't apologize up front for making a mistake in my own work, for "writing code that does not work" or other things which could be interpreted as being the result of my lack of skill in my work, making mistakes is part of it, and fixing mistakes are too.
I will be the first to apologize for messing up something for someone else, or giving bad advice, or for taking a decision which lead other people down a wrong path.
I'll also apologize, as soon as possible, and in front of others if they're there, if I said something that could be misunderstood or sounded harsh or brash. (Though, that really does not happen very often at all).
I believe in modesty and dignity, and apologizing is part of that.
This is a... tough question to answer. Do I apologise? Yes. Is it a sincere apology for wasting time? Not really.
I can explain better with examples.
"Sorry for wasting your time with this mistake," feels very formal and isn't really applicable in most cases. It would be more appropriate if, say, I'd made a mistake, not owned up to it, and the lack of accountability has a negative impact.
"Ah shit, that's totally broken. Sorry, that was my bad!" is more what I'd do and it's a lot less formal. I'm not really apologising or feeling any remorse. I didn't do anything immoral, here. What I'm really saying with "sorry" is "I am accountable for making this mistake and I will commit to fixing it."
I'd only apologize for something that I should have known given the information I had at the time.
Most mistakes are only mistakes in retrospect, but at the time seemed like good or at least reasonable ideas. I don't apologize if I've done my due diligence at the time.
And I'm Canadian, saying sorry is like our favourite pastime :)
That said, sometimes I'll convey that I wished I had seen things better in the past, and sometimes that comes out like an apology (eg:sorry folks, I wish I had known this tech was totally unsuitable here).
I have a hard rule of not apologizing for honest mistakes. If I took a decision with the best intentions and it was the right call with all the knowledge I had at the time, I don't apologize for it.
I do apologize for mistakes due to laziness, shortcuts, emotionally charged decisions and the like. Things I knew at the time (or could have known) were not the optimal choice.
