Theory is when you know everything, but nothing works,
Practice is when everything works but no one knows why.
In our lab, Theory and Practice are combined: nothing works and no one knows why!
- In Theory there is no difference between Theory and Practice, in Practice there is! [1]
- Simulation is like masturbation: the more you do it, the more you think it is the real thing! or:
- Simulation is like masturbation: if that’s all you do, you think that’s all there is. [2]
- “If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. If you can’t control it, you can’t improve it.” [3]
these are my favorites i often mention in my classes, there are many more, see also Fact and theory
[1] van de Snepscheut, [2] M. Athans, MIT, [3] H. James Harrington
Steinbuch 
Ha!ha!ha!
“The difference between practice and theory, is greater in practice than in theory.” would be my preference.
theory comes from the practice, the practice is theorized that in order to keep a less complicated model it may be omitted “small” details