Limitations of Proof-of-Work
Proof-of-Work is a revolutionary invention that helps with aligning incentives in a decentralized network composed of unknowing or even untrusting parties. It powers the Bitcoin network and kicked off a wave of innovations in the blockchain space.
However, it is not a very scalable nor sustainable mechanism and not suited to power networks set out for mass usage. Sustaining the Bitcoin network consumes as much energy annually as whole countries such as Switzerland.