A good platform is the foundation to anything built upon, operating within it or reasoned from it.... For example a building needs a solid foundation, water is a universal medium in which biological processes take place and logic is the foundation to thought. If the platform is sound, you can expect predictable and stable results. That does not mean that everything coming after will work or be suitable, in fact over time, the platform may become unfit for purpose or present limiting factors.
A platform might have a highly specific purpose and fulfill that function extremely well but will have no potential for changing it's scope......like a foundation designed for a two-storey building. If you continue to build upwards, the foundation and building will fail. The better the understanding of what you are building, the better the platform you are building is likely to be.
Water is a medium in which a plethora of biological processes can occur. However, the processes have evolved in ways that are perhaps limited by the medium in which they must occur. The fact that life is amazing speaks to the suitability and flexibility of water as a platform or foundation for building complexity.
BitShares is being consciously built and a great deal of thought has gone into it's design to make sure it is fit for purpose. What purpose does BitShares attempt to fulfill that would make it a suitable platform? It is a set of transparent, peer reviewed rules for managing and recording the exchange of digital information. The nature of information and what we do with it requires us to TRUST that the information can be sent when and to whomever we choose, that the information will be identical between source and recipient and that the record of that information can never be altered. BitShares, mindful of being an information exchange network that endures, seeks also to remain adaptable. In order to maintain trust, there are rules for how the rules can be adjusted. All of these rules ensure that over time, the platform can be trusted to resist changes that interfere with the core expectations of participants.
Other features of BitShares that make it suitable as a digital information exchange and record keeping platform are it's tx speed, ability to scale, software building tools, security, sufficient decentralization, transparency, support of personal privacy, utility as money, contract execution capabilities, ability to fund development.....etc etc.
Any project hoping to be such a platform must have rules and governance that inspire TRUST first, then maximum utility (a broad, scalable feature set) second.