But do not speculate - unless you intend to permanently start lowering the number of your bitcoins, do not sell.
I think its also a good advice to take some profits when you have been in for long and the price has been going parabolic too quick, or has been above the trendline for too long - for example, if you already have a x100 unrealized profit I'd recommend to sell 20% of your coins and thus recoup your fiat investment in full while cashing in a nice profit, I think that helps most people to be more rational and thus to have stronger hands.
Mathematically if you
don't know how many months it will stay above trend, then you
can't know when you sell whether you will be able to buy back in for a lower price.
When to buy has the same problem. There is only one exception I can think of. If you just obtained the money or ability to buy and you notice the price is below trend, then you are lucky and should buy immediately.
The only mathematical reason to sell is when you are ready to exit. And for larger holders, that should be sufficiently long duration before the expected final peak price and market cap saturation.
My friendly advice to AnonyMint: distopian future or not; world reserve currency or just "the mother of all bubbles"; disruptive community effort or trojan horse, I'd say that you just cannot afford to lose the opportunity of being into BITCOIN.
There are some factors that I can afford to lose.
1. Losing all my money because I lose the keys or they are hacked. Considering how busy I am, and health issues, etc.. I have to make choices about where to put my limited time. I lost $75,000 in 2012 because I was out-of-mind I was so near death.
2. Losing a lot of the money because of getting caught in a pincher again where I can't execute a sale for various reasons as I explained above. I am not sitting in a first world country with all status all perfectly in compliance as you all may be. I have an ex to deal with too, which complicates, etc..
3. The times where I made big money is where I did not spend any time on money, and all my time programming. I believe this will be the case again. I might forsake a 10X gain only before I will turn some code into a $1 billion in 2014. As if I really need that much, I wouldn't even know what to spend it on.
4. What I need most is about $2-3 million and anonymity so I can live my life in peace. I don't need more potential points of failure in my life right now, I have too many issues that can go awry already. K.I.S.S.
5. I have seen in my life I was forced to sell short-term by factors. Selling short-term into a correction is painful.
From your perspective yes, because that is the only opportunity you have. I am special. Sorry to say. This has presented me a huge opportunity just fell into my lap.
Nevertheless if I have not succeeded by Jan 1, I might buy some Bitcoin, perhaps up to $40,000 or so. Especially it might be below the trendline by then or Feb. which would reduce short-term risk of a holding.
Just throw at BTC the money you can comfortably afford to lose, historically it never let down those that took that choice. Do not be fooled by your greed that will tell you "x10 of a little is still a little", because if BTC realizes its potential the exchange rate will grow by many orders of magnitude - quickly.
It is not greed of 10X of a little. Rather the issues above.
Thanks for your concern.