A short squeeze typically occurs due to a combination of factors:

High Short Interest: A significant number of investors have shorted a particular stock, meaning they have borrowed shares and sold them with the expectation that the stock's price will decrease, allowing them to repurchase the shares at a lower price and profit from the difference.
Positive News or Catalyst: Unexpected positive news or developments related to the company can trigger a sudden increase in buying interest, causing the stock price to rise. This can include strong earnings reports, new product announcements, favorable regulatory decisions, or merger and acquisition news.
Buying Pressure: As the stock price starts to rise, short sellers begin to feel pressure to cover their positions to limit their losses. They are forced to buy back the shares they borrowed and sold, adding to the buying pressure and further driving up the stock price.
Liquidity Concerns: In some cases, short squeezes can be exacerbated by a lack of liquidity in the market, making it difficult for short sellers to find shares to buy back at a reasonable price. This scarcity of available shares can intensify the buying pressure and lead to even larger price spikes.
Market Psychology: As the stock price continues to rise, other investors, including those who were not initially involved in the short selling, may start buying the stock in anticipation of further price increases. This can create a self-reinforcing cycle of buying activity, pushing the stock price even higher.

Overall, a short squeeze happens when a combination of factors leads to a rapid increase in buying pressure for a heavily shorted stock, forcing short sellers to cover their positions by buying back shares and further fueling the upward momentum in the stock price.