In medio stat virtus (or, less commonly, in medio virtus stat) is a popular Latin phrase meaning «virtue is in the middle». The sentence is an invite to search for balance in things, which is in the middle of two extremes[1].
The expression comes from Medieval philosophy, but the same concept can be found previously in history: Aristotle in Ethica Nicomachea ("μέσον τε καὶ ἄριστον"; translated: middle is the best thing), Horace in Satires (Horace) ("est modus in rebus"; translated: there is a limit in things) e Ovid in Metamorphoses ("medio tutissimus ibis"; translated: you will go most safely by the middle course[1]).