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I partially disagree with you that most of the bitcoins that would be out of circulation would be as a result of the demise of some holders of bitcoin. There are thousands of people holding bitcoin, and no one is foolish enough to think that he would not have any preparation for securing his bitcoin for his heirs to inherit. At least not in this era, so many solutions have been brought to harness this situation of losing funds after the death of someone. Many bitcoin wallets have been dormant but were later considered to be lost. Yet after ten years, we would see a transaction taking place in that wallet. How come? Maybe someone found out the lost or hidden key phrase.
In the future one main thing that will reduce circulation is mass adoption and holding long encouragement. Imagine if 25% of the global circulation buys bitcoin; there will not be enough to circulate if this set of people and the previous investors hold their coins for 10 years or more. There will be a very high demand for bitcoin but no one will accept to selK. This will cause to the increase in value.
It's up to you how you react to it, but I think some people forget or delay telling their family that they invested in Bitcoin and suddenly they died. then his family certainly couldn't access his btc if he didn't tell them his private wallet key. In this case, I saw several articles which stated that several large BTC holders had died, but I didn't know in detail that the BTC holders did not leave their private keys to their families. So, for that reason, let's just take the point that BTC circulation will disappear because of those who die or those who can't access their wallet because the private key is lost.
So what is the advantage of all of this? Of course, the smaller the circulation and the increased adoption or the more people who invest in Bitcoin, the more visible the opportunity is for a significant price jump. I hope you understand what I am clear about and that there are no stupid people in this developing era, but please know that sometimes it is their carelessness that loses their assets, such as storing the private key incorrectly.
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If you spend, 10 to 20 to 30 years investing into bitcoin, and if you start out with bitcoin as your only investment, surely in the first 5-10 years there may be periods in which you might feel that you are not making progress, but then at some point you might start to feel that you have enough BTC,. and even if you are not quite at the level in which you are going to want to start to cash out some of your BTC, you might at least start to choose to invest into other things so that you feel less overexposed to bitcoin.
And mostly HOLDing through a period in which BTC prices go way up and way down takes a bit of commitment to the idea that it is just better to mostly be HOLDing. You likely have to have systems in place that allow you to do such a thing, and there are quite a few bitcoiners who are similar to me, and some of them were on this forum complaining that they did not sell more during the peak.. so sometimes there can be some regrets about missing such BIG trade opportunities, but even if you sell, you could end up selling too soon and then also not really know how to play it.. when to buy back and how to buy back, so it surely can be difficult to get anywhere close to the top in terms of selling and to get anywhere near the bottom in terms of using those proceeds to buy back.... so sometimes there can be more comfort in terms of not even trying to play those kinds of games with your BTC, unless you are just using a small portion of your BTC to do that, but at the same time, if you have not reached your accumulation target, it makes even less sense to be selling if you feel that you don't yet have enough BTC.
Yes, as long as there is no urgent need, of course it is better to continue holding. Indeed, 30 years is a long time and perhaps no one knows our future fate. It seems that if you have reached satisfaction, there will be an option to cash out and maybe it will only be a small amount without having to sell everything. Personally, the bitcoin investment journey is like drinking coffee every day where I keep doing it to keep buying and holding it.