Thats your typical small 'investor' or speculator in every market mainstream or crypto and its all the same because people are driven in the same way vs prices and news flow. Hence the overall market is a natural phenomena and can be predicted. The reason being the common factor is emotional guidance in decisions rather then something independent that gives a system to buy and sell. The ideal or the closest an average punter will achieve is to buy into a lull or anticipated low in the price and scale out during hype or rapid steep gradient BTC events.
Dont ever imagine you can capture the absolute low or be a seller at the highest prices, these are most often sharp brief prices and dont always have the most volume. Usually after the low or peak there will be a confirmation or retest of that price and thats when its reasonable to aim to capture a price to sell or buy at.
To answer the OP I would never sell all BTC because the market overall has such growth that it reoccurs over years even if we peak in 2020 or next year it'll still continue as a sector in growth for years. If I change my mind on that then I might try to guess and sell all along the way but otherwise I believe that to be the wrong decision. In general I just hope to lean more on the buys while we are quiet and relatively low, then lean into selling a bit more while we rise. I dont have the confidence to think I know the future top price and in any case I have needs elsewhere and its fair to just use BTC like it supposed to be used in transactions and payments. I hope we never stop using BTC to be secure online basically, thats its unique strength and reason to grow.