"Building on someone else's platform is a good idea, if you have your eyes wide open," investor Fred Wilson told a packed room of entrepreneurs on Monday night at an Internet Week event in New York City. He was answering a question about whether or not it's a good idea for startups to build on another company's platform, and we caught his response in the video above. Wilson knows a lot about this subject. He sits on Twitter's board and a year ago wrote a blog post warning startups in the Twitter ecosystem ti stop "filling holes." Twitter then proceeded to fill those holes itself by buying or building various clients and other services, and is still filling them to this day (its new pictures feature is a case in point). While this issue has created a lot of angst in the developer community, Wilson is very straightforward about it. "You should expect eventually the platforms you are building on to do something against your interest. One day you may wake up and discover that platform is competing with you, and that sucks."