We need to buy when the price is low but it is hard to find the bottom line of the price level that is why people are saying do your own research.For me I will start buying bitcoin when there is a positive news about bitcoin and sell when there is a negative news about bitcoin because normally the price will dump and bump according to the news about bitcoin.
We either buy when the market is down or we buy in bulk. The reason is that when the market is red, the purchasing power of the money we have is more and we can buy more goods and servises that we could before. Secondly, even if the market is not down, if you purchase in bulk, your average cost is redused as a result of which you spend less than you would have spent if the amount of the goods bought were not huge.