I don't know why the concept of "buy low, sell high" is so hard to understand. The point being if the the value for whatever you have bought has plummeted (particularly if it drops below what you bought it at), then it is already too late and obviously not the right time to sell. You might as well take your chances and wait for it to bounce back vs. panicking and selling.

As far as cryptocurrencies are concerned, I don't really have money to invest in them so all I have invested are computer resources for mining and my own time participating in this platform. From my point of view it isn't the right time to sell until and unless I end up accumulating a life altering amount (or I'm making enough on a daily basis that it makes sense to cash out part of it on a regular basis as an income). I figure I'm better off sticking with the cryptocurrencies I have an interest in (currently bitcoin, steem, gridcoin) vs. selling and speculating on ones I'm going to pay less attention to. But then I don't invest for a living :)