This works to validate transactions because it makes it incredibly difficult for someone to create an alternative block or chain of blocks. They would have to convince everyone on the network that theirs is the correct one, the one that contains sufficient proof of work. Because everyone else is also working on the 'true' chain, it would take a tremendous amount of CPU power to beat them. One of the biggest fears of Bitcoin is that one group may gain 51% control of the blockchain and then be able to influence it to their advantage, although thankfully this has been prevented so far. Or continue reading this article for free Benetton, M. & Copiani, G. 2021. Investors’ Beliefs and Cryptocurrency Prices. Working Paper, Yale University. https://cowles.yale.edu/3a/bcwp-investors-beliefs-and-asset-prices-structural-model-cryptocurrency-demand.pdf.