The direct detection of gravitational waves marks the beginning of a new era for physics and astronomy, with an opportunity to probe gravity at its most fundamental level. I will discuss the subtle interplay between the behaviour of gravity as we observe it at low energies, and its embedding within a meaningful high energy completion. In particular, I will emphasize how causality is manifested with gravity, a consideration which is particularly relevant for putting constraints on the physical theories we use to describe observations and make future predictions.