The central task as a data engineer is: give me whatever data you have in a variety of formats, volume, and velocity and I got it, and I'll take care of it.
Designing efficient schemas that scale is a core job responsibility of any data engineering team.
The given data comes from a data source and as a data engineer, you need to build those reliable ways of retrieving and storing that data. Those are your data sinks, the first line of defense in an enterprise data environment is your data lake.
Data engineers design and build data pipelines to transfer data into OLTP (Online Transaction Processing) systems or OLAP (Online Analytical Processing).
It's up to the data engineer to ensure there are no bugs in the data pipeline that would cause such a result.
Unifying programming and processing is a big innovation in Data Engineering.