Rallies can happen for a variety of reasons. Investors may flock to a company's stock before a big or highly anticipated announcement, such as the release of a new iPhone from Apple or a new car from Tesla.

They would do this to benefit from the launch of the new product and the increased revenue generated by sales. As a result, the stock's price will rise as demand begins to outstrip supply.

Longer-term rallies can also be triggered by larger-scale economic events such as changes in government tax policy, interest rates, regulations, and other fiscal policies. Any data that indicates a positive shift will almost certainly cause traders to rally behind those investments that may be impacted by any deviation from the status quo.