I'm fairly lenient.

I can't read minds, so if someone is technically wrong (or wrong in my
opinion), I will never down-vote them. My reason is simple; they might
be entirely sincere and believe they're contributing even though they're
unknowingly wrong and unfortunately spreading misinformation. If I have
better information, I post it, politely, and with references if at all
possible. If it's a matter of differing opinions (not facts), then it's
best to just quietly let it slide. I didn't come here for an argument,
or lessons in getting hit over the head (sorry for the Monte Python
reference).

Additionally, I don't need to agree with someone to appreciate the time
they took to share and post their views. Even if I never agree with
them, I benefit from knowing how the other side(s) sees things.

If someone is being rude or intentionally insulting, that's good for at
least a down-vote, and possibly a flag if it's egregious.

Both flagging too much, and down-voting too much does have effects on
your account. The precise mechanics including the value of "too much"
have never been made public. I can't prove this in code that's actually
running on HN (no public), but there's an ancient post by pg that
mentions it. I could probably dig it up from my notes if anyone needs
further confirmation... But, who's to say pg hasn't changed things in
the years between that old post and now?

It makes sense that there's a price to pay for abusive flagging and
down-voting. If you spend a lot of time on the 'new' page (/newest
queue) and flag the spam as it happens, you could very well trip the
abusive flagging threshold. On the other hand, if you do trip the
threshold, and pg/mods see that you're actually trying to help out with
the spam, they'll be thankful rather than upset.

Some down-votes are entirely unintentional. The voting UI/UX has issues
in mobile environments where small screens and large fingers result in
miscast votes. It wasn't so long ago that I saw Joey Flores (YC funded -
earbits.com) apologize to pg for accidentally down-voting him, so it
indeed happens to the very best of HN users.

As you might expect, the result of miscast votes is some voting patterns
you see are actually somewhat random. Adding to the randomness are
language barriers causing misinterpretations. Also adding to the
randomness are quickly written and poorly communicated comments. Even
when you mean well, others might not understand what you wrote.

Off the top of my head, I think it was you (001sky) who recently replied
to one of my posts, and I didn't really understand your comment... Yep,
it was you:

https://news.ycombinator.com/item?id=4493615

Maybe it's written perfectly and I'm the sole cause of my failure to
understand? ;-) But anyhow, the point is, miscommunication happens
constantly and it is one of the causes of down-votes.

My ability to type comes and goes due to my health, so I don't post or
contribute very much. When I do post, I rarely get down-voted. I might
get one down-vote in fifty posts or so. I do keep a very close eye on
the score of my posts, and if I notice a down-vote, I'll dig in my
comments to see where it occurred. Since I know about the randomness
problems in voting patterns, I never take a down-vote personally. For
all I know, it could have been an intended up-vote that went wrong, or
someone in the habit of down-voting for mere disagreement of opinions.

Even if someone down-votes me out of mere disagreement, it's still
useful feedback.

The best practice for debates on matters of contention is simple; be
certain to give the other person both polite respect and the benefit of
the doubt on their intentions. Some people will still react in rude
and insulting ways if you politely pose a tough question, or dare to
offer an opposing view to their imaginary authority.

https://news.ycombinator.com/item?id=4489017

It's just one of the risks to open forums. Some people think being rude
and insulting (i.e. "mean" in pg-speak) will somehow make their point
more convincing and help them "win" --whatever that means. It's very
unfortunate, but it's just part of life when interacting with others.