Bitcoin is and always will be very volatile, but this does not mean having to give up his purchase. If you look at the chart of growth rates you will see that every year the price of bitcoin is increasing. This trend will persist for a very long time so you can buy it at any time.
so i should buy bitcoin at this point or when the value reduce.
You should look into buying it when theres something that effects the market, like the Chinese new year that was going and the prices dropped low on that month and it raised back to 11K as we speak.
It is not good to be confused about bitcoin it is nature of bitcoin that it use to increase and decrease with time so just look at the market if in maker price is down it mean you should buy and it is time to save it but if they demand of bitcoin in market is high and price is increasing too then you should sell for profit, on the other hand I would say that instability and fluctuation is the best thing about bitcoin, bitcoin is volatile and it will make price of bitcoin at the peak of all other currencies.
According to my experience, I have some factors to know the next short time trending for any cryptocurrency, not only Bitcoin:
1. When the Bitcoin trading volume increased higher 80% than normal but the value of Bitcoin has changed below 1-3%, that is the time to buy Bitcoin as soon as you can.
2. When the Bitcoin trading volume increased or decreased more 80%-50% than normal but the value of Bitcoin has changed more 5-10%, that is the time to sell Bitcoin as soon as you can, even you must to take loss, because the big bearish trend will happend in the next time.
BTW, please give me some merits if you think my experience useful for your trading

, thanks a lot.