Vitalik Buterin, co-founder of Ethereum, has published his latest article "The Future of the Ethereum Protocol (Part 5): The Purge", which states that one of the challenges facing Ethereum is that by default, the bloat and complexity of any blockchain protocol grows over time. This happens in two places: historical data and protocol characteristics. In order for Ethereum to be sustainable in the long term, strong counter-pressure needs to be applied to both trends, reducing complexity and bloat over time. But at the same time, one of the great features of blockchain needs to be preserved: permanence. The key goal of The Purge is to reduce the storage requirements of clients by reducing or eliminating the need for each node to store all history permanently, and possibly even eventually declare; to reduce protocol complexity by eliminating unwanted functionality.