ELI5 how people make expectations of future market performance based on what the Fed does

I admit, I’m a fairly new investor. This is my second year in the stock market, and yes, this is my first bear market. So far, I’ve been enjoying it. I’ve put extra capital aside for this moment. It feels great being able to purchase stocks I thought were good value 6 months ago for even cheaper.

I understand how inflation and rising interest rates affect the economy, but I don’t quite get when people say that the Fed doing things such as reducing their balance sheet or QE will cause a serious market crash or words to that effect.

For those that are still expecting a further crash or are thinking that this is the bottom based on what the Fed has said, please could you ELI5 as to why you hold that opinion? Thanks in advance.