I bought in the mid 50's. I'm not concerned about being underwater today, but in the ride up there will clearly be frequent predictable 10-20K drops, so I should not hold at $55K. It may pay to keep trading it up. Meaning I should next sell at 60K + and buy at 55K then sell at 70k and buy at 60k. This is a predictable pattern for BTC, no?
That depends on how surely you can predict the next high or the next low. It is not really predictable but the swings are much more than other trading places like the stock market.
Many people who have been doing this for a long time would also tell you that it is better to just HODL. What some of us do is to keep a part exclusively in BTC. That stash is only meant to be added to and not fiddled with. So we buy the dips and don't touch it. The other part can be your play money to have "fun" with and compound that portfolio by buying low and selling high. Mighty hard to do for even the best traders. Those who do it consistently, tend to keep the secret.