"当我们开始时，我们思考了互联网的规模——如果每个人同时使用这项服务，那会是什么样子？"

Simplified Meaning:

Imagine you are organizing a big community event, like a concert in the park. Before you start planning, you need to think about how many people might come. If the whole community decided to attend, the park would need lots of space, enough food stalls, and plenty of toilets so everyone could have a good time. You wouldn’t want long lines or people feeling cramped. This is what the quote is getting at. When they began their project, they thought big. They imagined everyone using their service all at once. By thinking on such a large scale, they made sure to plan for a service that could handle lots of users smoothly. This way, when many people showed up to use the service, everything would still work perfectly. This is a smart way of planning that prevents problems before they even start, just like having enough supplies and space at a big event.