My pick is Jeff Dean's The Tail At Scale (2013) [1]. If you're interested in performance of web services, it's very, very well-written and describes a counterintuitive (but crucial!) phenomenon: your p99.99 latency can drive the entire user experience because of head-of-line blocking. As microservice architectures have gotten more popular, this has only become more important.
It's a fiendishly difficult problem to get around, but Dean proposes a few mechanisms. I learned a lot and think back to this paper often when designing real software.
Reading it will probably make you a better engineer.