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Based on adoption. Why is Bitcoin so high in price? Finite supply, high demand. While the supply of STEEM and SBD is a lot higher than Bitcoin, the adoption curve, as you can see from the number of new users joining, plus the amount of interactions with the platform (upvotes, posts, comments, etc.) and the underlying technology behind it, the STEEM blockchain, which currently has the most transactions per day than any other blockchain (like Bitcoin, Ethereum, etc.) and also the scalability of it, and the roll-out of Smart Media Tokens (basically monetizing other media platforms) and the ability to create ICOs (new tokens) on the STEEM blockchain (example Vice ICO for adult media) is what brings value to STEEM. The community, and the rewards that people gain (the money they make) is also the fundamental aspect that fuels the STEEM ecosystem and economy.

Steemit.com was just the first step, as a blogging platform. We now have DTube (video) DSound (music) and DLive (live streaming) platforms all created on the STEEM blockchain. Who knows what's next? The only thing we're certain about is the scalability and the mass-adoption of the STEEM blockchain through all these media channels.