The ISRG’s goal for Let’s Encrypt is to bring the Web up to a 100% encryption rate. When Let’s Encrypt launched in 2015, the idea was pretty outré—at that time, a bit more than a third of all Web traffic was encrypted, with the rest being plain text HTTP. There were significant barriers to HTTPS adoption—for one thing, it cost money. But more importantly, it cost a significant amount of time and human effort, both of which are in limited supply.
Let’s Encrypt solved the money barrier by offering its services free of charge. More importantly, by establishing a stable protocol to access them, it enabled the Electronic Frontier Foundation to build and provide Certbot, an open source, free-to-use tool that automates the process of obtaining certificates, installing them, configuring webservers to use them, and automatically renewing them.