+1. On modern hardware and software systems, performance is effectively stochastic to some degree, as small random perturbations to the input (code, data, envir

+1. On modern hardware and software systems, performance is effectively stochastic to some degree, as small random perturbations to the input (code, data, environments, etc) can have arbitrary effects for the performance. This means you can't draw a direct causal chain / mechanism from what you changed to the performance change - when it matters, you do need to do a deeper analysis and investigation to find the actual and full causal chain. I.e. a correlation is not a causation, and especially more so on modern hardware and software systems.