For example, let's say I believe BTC will go down. So I BUY BTC. And then I wait for it to go down and then SELL.
Don't I lose money?
When you believe a particular coin price will go down; you don't buy again, you short the trade which we refer to as sell. It's definitely not for everyone because of it high risk. It looks good in theory but a very dangerous strategy because once you short your trade and the market price start appreciating, is your money that is gradually liquidating as the price increases.
Some who is a trader knows what to do at any given point of time, but someone is a novice in trading doesn't know what to do at any point of time, I know very well that trading that trading is a skill someone who is interested or desperate in trading have to learn and understand the basis before joining, as I stipulate in my first response here, anyone who want to trade and always try to be in positive side of the market have to know when to enter market and when to quit from the Market, and one of the tools that will help to know the preferable time to be in the market is when you have understand the system by learning the chart and understanding the movement of candles sticks in chart, when you are able to understand this primary thing in trading I think you don't need to be fare of when to be in the market and when to leave the market.