Yeah I think it is nice to talk to you because it is like reviewing my own behavior at the tables, but then somebody else is doing it : ) I realized everything in life happens in a spectrum you know, and you can be too loose or too nitty, and the optimum, which is dependent on the person, the table, the stakes, the individual opponents, lies somewhere in between. Against player A your optimum should lie here, and against player B somewhere else; yes it is difficult but also keeps it dynamic and interesting.
If I can add something from my own experience, I used to think that just because the board paired and my opponent bet big, this had to mean that either the paired board helped him or at least not fear it because he would see that the board just paired right?? and wouldnt he then have to fear a full house by someone else? But now I realize that it is so important not to just look at the river in a (nitty) vaccuum you know, and be like paired board = throw away nut flush, but you should look if you think it makes sense the way your opponent played up until the point that the board paired if it is likely he made a full house + (it has to be at least a full house for you beat all other hands) and then I would almost always come to the conclusion that the way it was played until the board paired actually made it UNlikely the 8 on the river filled someone up. Your opponent might also have thought that you didn't fill up on river, and he would have been right about that.
Also we should NEVER underestimate what effect our behavior has on that of our opponents... a check on the river will set the door wide open to all kinds of nastiness you know. Try to think what your check will mean to your opponent, and also try to think what your line will be BEFORE you make a move (and not start thinking until after our opponent has already made his move):
will you check fold or check call if you plan on checking, and if so, why??
do you think by checking our opponent will be affected in his behavior as in will our check make him do things he would not dare if we had simply bet into him?
if you lead out, what are you expecting your opponent to do in reaction to our bet?
here betsizing is also important, as a small bet could still get raised by the King high flush.
and lastly if you bet will you still fold if you get raised? or do you consider yourself potcommited after leading out into our opponent?
and why dont we go all in, do we really think we are only going to get called by worse? if you think all lower flushes will fold to an all in and only full house plus hands will call us, then of course you should not donk all in.
Once again when leading out, consider betsizing and be careful with these kind of "bet small so we still have an exit strategy" as they can backfire on us what happened in the KKK example. Sometimes it is good to still have an exit strategy, sometimes, we should not consider an exit (strategy) as a viable option anymore and just go for broke, at least when you do it AFTER you weighed your options, it is most of the times the right thing to do; it is up to you to decide when to do what.
Imagine you had called all in, you would probably be like oh no what if I am beat, until you see like $15 shipped your way and see villain has K high flush and loses hero wins with A high flush and then you are like OMG I almost folded this! : ) As you can tell, you are talking to someone with very similar experiences to yours here.