Bitcoin market is something no one can actually tell when it is best to buy or hold instead you buy when you have what it takes to and wait for the outcome. From my little experience I think every time is best to buy and hold Bitcoin all you need is Patience...
You are wrong in your statement here. Bitcoin is somthing you can know when to buy. You can also know when to hold. It is simple to buy low depending on the difference prices bitcoin has attained and the ATH. When to hold it not really affected by the price condition but how long you are willing to leave your investment in bitcoin.
The factor that makes it difficult to determine is actually when to sell, anyone that has an investment plan should also know the right time he stipulated to exit the market and when that time comes, the best thing is to exit to avoid indecisions.