Such an indicator does not exist. Indicators only indicate the movement possibility but does not confirm it. 50% cases it goes as the indicator goes but in 50% cases it might not. So this is not an exact science but a way or predicting the future.
50:50 is like gambling but I understand your example. Even if rate of success is more than 50%, like 70% or 80%, if a person has bad risk and capital management, 20% or 30% of failure can take all initial capital after some rounds of failure.
Management on capital and risk is most important to keep initial capital safely and from secure initial capital successfully, it's foundation of something better.
Strategies dont need to change often. From what I have seen, stick to buying low selling high and setting stop losses. These three things if timed and executed properly will save a lot of money and allow you to make profit in between.
One strategy can work well most of times but if a person have poor capital management, bad risk management, one or two failures can take all money in liquidations.
Senior investors and traders will advice, "Always prioritize protection on your capital, it's most important thing to do, rather than try to find profit". If you exit the market, keep your capital safely, you can miss an opportunity but you will have many other chances in the market in future. Don't be fearful of missing opportunities and ignore risk, then fail to protect your capital. Without capital, you can not do anything even opportunities appear.