RE: This is getting like the 100p12 Mar 2021 22:00
Charts don't predict the future; they simply tell you what has happened.
You can deduce from it some level of market behavior and assume different cases going forward. The strength of chart analysis is that it can lead to self full-filling prophecy; because many will be using the same techniques and data points. That is why most use the same moving averages 20, 50, 200, same RSI, MACD, etc...
Very simplistic Example, many will be looking at the 20day crossing above the 50day or the 50day crossing the 200day as a buying signal for an upward trend; but so are many other people, a mass of people then buy in which causes the SP to go up. But the rally then looses momentum for many reasons and when the 20day crosses below the 50day many will start to sell which then drives the SP down. If every used a custom average then the chart analysis would not be as effective.
Similar when the SP goes sideways and support and resistance lines are created; people will set their entry based on the support line which causes the SP to go up and many set exit at the resistance level which reverses it.
Obviously there are other external factors and news that come in to play that break those behaviors and add the unpredictability.