Well, there you go again with the word "know". There is some evidence that skin in the game provides for better prediction power. For example, prediction markets tend to outperform the polls.
Not to sound cynical, but "price action" and "sentiment" don't really have much predictive power. Most of such predictions are not worth the tea leaves that are being used. The fact that you (or someone) was right X-teen years ago does not really make it a scientifically valid method. A frequently mis-attributed proverb says "it's hard to make predictions, especially about the future".
Possible. IMHO, an adult view is not to be die-hard anything and change your opinion based on the evidence. I think that's what differentiates a good pro from an amateur in this business (with some really prominent managers behaving like total clowns in that regard, of course). Of course, that would make one a "flip-flop" and frequently would require admitting defeat. My personal trick is to internally express any view as a numeric probability and adjusted it based on the new evidence. Makes it much easier to change my opinion without damaging my ego
People without positions exhibit similar confirmation biases, as has been illustrated in this thread. Seems like confirmation bias is about being right more than anything else. In general, these forums are a wonderful illustration of what biases we all carry (especially if you stumble into the politics section, not that I'd advise that), confirmation bias being the mother of them all.
On the topic of bitcoin, fuck knows where it will end up. I think I've stated before that it probably will settle somewhere in the 7 to 15 thousand range, but we can easily see both 5k and 50k while we getting there. At the time I had a whopping 5 coin position that I carried from just over 500 dollars, so I had put some thought into it. For the record, I unloaded it in the middle of January at 13 and some pennies. The thesis was unchanged but my favorite dog rescue urgently needed 50 grand to keep them afloat.