Salir is one of those verbs whose meaning changes when used pronominally. The presence of the so-called se aspectual changes the meaning to an unexpected, improper and spontaneous action –instigated by the subject itself, either intentionally or by accident. Additionally, 'salirse' requires that the subject be a delimited entity, made clear by a determiner (el, este, etc.). [See also: salirse de madre & salirse de la regla].
-El agua salió del grifo — The water came out of the tap [Straight fact]
→El agua se salió del grifo — The water leaked/burst out of the tap [Unintentional, unexpected, unwanted]
-El coche salió de la autovía — The car left the highway [Straight fact]
→El coche se salió de la autovía — The car came off the road [Unintentional, unexpected, unwanted]
-Salí del cine — I went out of/left the cinema [Straight fact]
→Me salí del cine — I walked out of the cinema [Intentional, spontaneous decision, unexpected, inappropriate, ill-timed]
-A veces uno necesita salir de su zona de confort — Sometimes you need to get out of your comfort zone
→ A veces uno necesita salirse de su zona de confort [In this example there is very little difference, but with 'salirse' it denotes overstepping an expected or permitted limit]
-Salió agua de la bañera — Water came out of the bath [Without determiner]
→Se salió el agua de la bañera — The water came out of/spilled out of/overflowed from the bath / The bath overflowed [With specific, delimited water]
