EIP-7 DelegateCall opcode allows a separate execution in another contract while maintaining the original execution context.
With this opcode, all message calls from the user will go through a Proxy contract.
The Proxy contract then redirects the calls to the Logic contract.
And when the logic contract needs fixing or upgrading, you just deploy that - HOWEVER - the implementation (the original deployed contract) of Proxy will remain the same.
You only need to update the address of Logic contract stored in Proxy contract.
The Proxy Contract uses Delegate calls and Solidity assembly because without it, it's impossible to return any value from delegatecall.