Everything should be made as simple as possible, but not simpler.
Based on Albert Einstein's works, but unsure Einstein wrote it like that.
A difficult quote to track. Lots of threads over the Internet deal with the authenticity of this quote (e.g. quoteinvestigator.com), but none of the recorded material from Einstein includes it.
But for practical purposes, it is a valuable quote: when modelling something, make sure to take into account all relevant aspects. It points to the importance of not ignoring things just because the modelling tool does not support it. If certain characteristic is relevant, is must be considered.
A topic/subject in computing is never a full model, but just a model with a goal in mind. The modelling of the subject need to include all aspects required to reach that goal ("not simpler"). Always without cutting corners, but without focusing on unnecessary things (here the "as simple as possible" part enters).
This means that, when a subject is modelled for a purpose, that model might not be enough to be applied for a different purpose; if that new purpose require other set of characteristics or just additional ones.
A quote that puts together modelling, simplicity, the path to complexity and the purpose of that model.
What a quote!