Stop limit orders are really only useful when selling coins. They allow us to set a condition: we specify a price, and if the price becomes less than or equal to that price, a market order is automatically placed for us. The advantage here is that if we need to step away and will not be able to watch the price, we have some protection if the market begins to plummet. The disadvantage is that we are counting on there being good buy orders available to fulfill our sells. If a massive amount of market sell orders were to be executed right before your stop is triggered, it’s technically possible to be left with the bottom of the barrel. This has happened before, but is not common.
No, the successful trader is not me. I’ve gotten lucky a few times and I’m still refining and trying out strategies; on the other hand, I’m part of communities of people who trade on a daily basis to grow their portfolios, and while some of the results can be attributed to luck, a majority of it is based on fundamentals, good habits, and experience.