To fully understand why we can never be 100% sure of what is going to happen in the markets we need to look at how the markets work. The price of assets go up and down because of traders either bidding the price higher or lower.
Every trader that places a trade has the potential to move the market.
Because it is others that make the price go up and down, for traders to place a winning trade they rely on other traders agreeing with what they think and acting in the same manner.
For example if I was to go short (PUT) I would be relying on other traders also going short (PUT) to make the market go short and make me a winner.
Because every trader has the potential to move the market we can also look at each and every trader as an individual factor in the market.
At any time there could be thousands of individual traders entering and leaving a certain trading asset.
The only way we could know exactly what is going to happen in the market is if we knew exactly what every single trader was going to do at exactly what time and price!
To think of it like this makes looking for a certain outcome in the markets pretty silly, but this is what people are expecting every time they look for a system that is 100% right!
Obviously knowing what every trader is going to do is impossible, so therefore knowing for 100% certainty what will happen next in the market is also impossible!