如果总是50%左右对，50%错，那和随机掷骰子没区别。说明完全没有形成postive return 的交易系统。

但是如果是100%错（假设只是long only trade）, 其实这说明交易系统已经是个半成品了，“买了就
错”意味着：1）比如你的系统是buy on reverse signal, 但你却用break out 的方法去交易，或者反之； 2）也可能是你的timing 把握的不对，或者止损太小，或者止盈太远；

100%错的时候千万别放弃，也许就是一寸窗户纸，捅破了就好了。

The reality is that buying an ETF on any exchange is essentially the same as buying the 3 to 5 largest weighted stocks within that ETF. If an investor isn't making money on those individual stocks, it's unlikely he'll make money on the ETF too.

Conversely, if someone can profit from buying an S&P 500 ETF, whether in the long or short term, he should also be able to profit from, e.g. THE "big-7" stocks too, given that these stocks are over 80% correlated (possibly even more than 90%) with the ETF. This principle applies to all index ETFs and their major component stocks.

I think the key to survive is to create a well-defined trading or investing plan, which should include the following elements:

1) Your Objectives: Are you aiming for short-term quick profits, or long-term steady growth, or something in between?
2) Your Buy-Sell Style: Your objectives will determine whether you engage in short-term speculation, mid-term trading, or long-term investing. (Speculation is a neutral word and not negative.)
3) Time Commitment: The amount of time you can dedicate to observing, studying, and buying/selling the market will significantly influence your trading (investment) style.
4) Product or Instrument Selection: points 1-3 list above will guide you in selecting the most suitable instruments. Consider factors like liquidity, volatility, trading zones, costs, bid-ask spreads, and more.
5) Detailed Buy-Sell Strategy: Define clear entry and exit criteria, lot sizes, holding periods, position sizing rules, and other relevant parameters. Whether your strategy is based on fundamental analysis, technical analysis, or a combination of both, it DOESN"T MATTER —as long as it's simple, consistent, and thoroughly tested. Not only trading needs a rule; Investing ALSO needs a very specific set of buy/sell RULEs.
6) Discipline: Without discipline, everything listed above is meaningless. Stick to your plan and execute it consistently. If one can't commit to this, one shouldn't even start.

亚马逊第一说的是“牛市买什么亏什么”。

这样的问题不在于选择了什么品种来做投资或者交易。而是就在于更具体的细枝末节没有考虑过，没有做过plan，所以才会出现上涨了的标的买了也会赔钱。

不在于“选择买了什么”，无论长线投资还是短炒，你总会有一个买的动作， hold 的动作（经历涨跌心理情绪波动的过程），无论hold 多久也最终会有卖的动作。任何一个参与市场的人都躲不掉。 即使买卖ETF也不是买一下就完事了。

比如25年dollar cost averaging strategy, 25年以内“打死也不卖”，就是一个铁的纪律，看似很简单，但是需要多少commitment,
每个月要定时买吧，如果下个月跌了10%，还敢不敢买？如果下个月涨了10%， 还敢不敢买？敢买的话买多少？买一样的数量吗？还是一旦跌了10%加码再买一倍？这钱25年内能不能保证不用到？如果出现了event driven的news, 比如前天英伟达或者前一阵microsoft 旗下宕机的事件要不要加码还是观望？还是卖出？25年这么长的时间随着自己收入的提高要不要隔两年就加码？还是把钱分到别的投资标的？什么极端情况可能会清仓？等等等等。。

以上我只是拿定投这一种常见的策略举个例子，这些问题在所有的投资或者投机中都是一定会出现的。当然一个投资者也可以完全不理这些东西，就走一步看一步再说呗。想买多少买多少，想卖多少卖多少，想啥时候买卖就啥时候买卖，看心情。
当然完全可以，没有对错。这是一个心理同时也是一个概率游戏。最后需要一点运气。如果能把心理建设的强大一点，把概率通过观察市场和学习增加一点，运气应该也不会总是那么差。