Question: This news about the Tesla stock came yesterday. The stock rose to 8% and then retreated. The following is the story.

My question is, what caused the stock to retreat other than a reason of a seller sold the stocks? Is it by a computer algorithm automatically adjusted before a few seconds before the real buying took place?

News: <https://www.marketwatch.com/story/telsas-stock-pares-gains-after-briefly-passing-first-key-fibonacci-retracement-level-2020-09-10>

Answer: 
Fibonacci Retracement (and most technical indicators, IMHO) is an *effect*, not a *cause*. It may work on average (meaning it predicts resistance correctly more often than it doesn't), but I highly doubt that there are many traders that say "Tesla passed this retreatment/resistence level so I'd better sell now." More likely there's some underlying cause that *creates* these technical indicators. It may be that some people were happy to see a gain and wanted to lock in gains in case it was temporary (which it was). Or there was reactionary buying at first but more selling as the market absorbed whatever news or rumor caused the buying. There may also be traders that sell when a stock reaches analysts' "price targets" and there are more targets clustered around certain numbers that can look like "resistance" when price movements are viewed on a graph.

In other words, there's not some magical computer algorithm or trading strategy that *creates* these patterns. The patterns themselves are an effect of some underlying market (or behavioral) patterns that are not as observable.
If you draw a matrix of lines on the price chart of a security, there's a a high probability that price movement will move to the vicinity of one of these arbitrary levels. It could be Fibonacci numbers or for that matter, you could just as well draw price ratio horizontal lines based prime numbers above and below current price.

The thing with support and resistance is that it's ambiguous. Based on the naked eye, it's a range of values in the vicinity of the price line and appears to work. But code that into some mathematical rules and back testing the strategy is a very different thing.