At a top or bottom, sentiment of the MAJORITY of market participants changes. Whether based on reality such as news, data, etc, or something perceived such as news, value, technicals, etc does not matter. When sentiment of the majority changes, a top or bottom occurs. An intraday top or bottom may or may not be meaningful to longer term market participants... therefore the size of the majority is not a constant. Everything within a context.
BPA stands for bisphenol A. BPA is an industrial chemical that has been used to make certain plastics and resins since the 1960s. BPA is found in polycarbonate plastics and epoxy resins. Polycarbonate plastics are often used in containers that store food and beverages, such as water bottles. They may also be used in other consumer goods. Epoxy resins are used to coat the inside of metal products, such as food cans, bottle tops and water supply lines. Some dental sealants and composites also may contain BPA. Some research has shown that BPA can seep into food or beverages from containers that are made with BPA. Exposure to BPA is a concern because of possible health effects of BPA on the brain, behavior and prostate gland of fetuses, infants and children. Additional research suggests a possible link between BPA and increased blood pressure.
1) My positions bleed. 2) My eyes cross. 3) My blood pressure spikes. 4) Appetite? Gone. 5) Telemarketers call. 6) I have to pee. Say, how many of these do you want? 7) My monitor chooses this moment to lose color rendering. 8) ...
... or, perhaps a little more accurately, the sentiment of the market participants trading the majority of volume changes. They're not necessarily the majority of market participants. "Just saying ..."
Sentiment changes for every reason under the sun. You will drive yourself crazy looking for exact cause and effect at these points. If you had access to market internals, such as order flow, perhaps you could anticipate turning points. Otherwise, as a retail guy, you can only react to what you see. Reactive versus proactive doesn't sound like a good choice, but what other alternative do you have?