If anyone can build your product in a weekend, what's actually defensible? The truth is, the kid in his dorm room now can quickly build the same product that your Series B Startup took 5 years to piece together. "We built it" is about as defensible as "we have a website." Congrats, so does my dentist. So if anything and everything can be built quickly, what's left to build that has real staying power? Are there any moats left? The answer is simple. The last real moat standing is this: An…