First off I never add "Not advise" because no one should be making any decisions based on an anonymous Internet posting. But people do act on ideas they read here all the time, but they have to make their own decisions.
I agree we may see the entire market tank as we did in 2008. As I have stated before unless I get out near the top I don't see the point to exit at some point on the ride down. Everyone is screwed and there really isn't a good place to park cash. It kills me that I have a fairly large cash cushion getting almost nothing as it is. But can anyone predict close to the bottom? When do you decide to buy back in? For me a lot of it also depends on the amount of taxes I'd have to pay. Even with capital gains rate, it would be a substantial amount for me for some of my positions like TSLA. Believe it or not I see that as a great position to be in. Hell the taxes alone would be more money than I ever imagined I'd ever have when I was a kid. On occasion I have cashed out portions of positions and then bought back in but that is not my usual strategy. I unloaded my Nintendo stock at one point even though I believed the stock had a real potential for future gains but it was tanking, with the idea of watching it go down and buy back in later, and that worked out well for me but stocks like TSLA and AAPL are so unfathomable at times that I can't see myself doing what you suggest. I am a buy and hold person, but I understand that many here are not, so they play the short term fluctuations.
I just don't see TSLA as being a bad bet at this point with what we know right now. People arguing that they may only have a run rate of 20,000 going out of 2017 and that is a bad thing strikes me as "who cares". Yes the average investor will probably panic because they aren't going to actually make 20k cars in a month until January 2018 so to them the entire year is a big fat loss so we may see another drop now or in December. But Tesla is going to build a sugarload of cars in 2018 so I won't sell.
Many years ago my broker used to call me a lot telling me that I had too much AAPL and it was more than 70% of my holdings which violated some market risk guidelines and I should rebalance. I took his advise and regretted it ever since. He no longer advises me about my holdings. I make those decisions for myself, good or bad. So for me I don't usually sell unless I am forced because of needing cash (which I don't see happening any time soon) or because I no longer have faith in a company. Were you able to time the 2008 crash? Selling near the peak and then what did you do with those funds until you felt it was ok to buy back in? To be honest if I knew the market was in fact going to slide downward for a year I would wholeheartedly agree with you and sell at the top, but I never saw it coming and kept expecting it to reverse. Cost me over a million dollars, but I just kept thinking it would reverse. I'm an idiot as I have said many times before. I just never understand the market herd mentality so I can't do that. I do understand that some here can discern the enigmatic workings of the market, but I think most of us can't do it successfully. So for me if I see TSLA down I see it as a buying opportunity. Yes some here are dangerous bulls who take the risk of buying on margin, but I hope they understand the risk they are taking on. My long term trading may not work for you and maybe TSLA or the Market in general is about to fall off a cliff but I'm not bright enough to play that dynamic. Everyone has to make their own decision on what they can risk. I don't do margin and I never bet anything I can't afford to lose. It has worked out well for me but everyone's situation is different and no one should blindly do what I do. But if TSLA is still in the low 350's on Wednesday I'm thinking I'm going to pickup another 100 shares.