There are probably a lot of programs that could be built in a weekend. I imagine any competent full-stack developer could make a Twitter clone in an afternoon.

There are probably a lot of programs that could be built in a weekend. I imagine any competent full-stack developer could make a Twitter clone in an afternoon. The challenge is making it scale. That developed-in-an-afternoon Twitter clone probably won't be able to handle an active user count in the 4 digits, let alone the 7+ digits Twitter has now.