TL;DR: If small changes have a big impact, you need to decouple your system.

Problems

• Coupling

Solutions

• Decouple.

• Cover with tests.

• Refactor and isolate what is changing.

• Depend on interfaces.

Examples

• Legacy Systems

Sample Code

Wrong

class Time(
    private val hour: Int,
    private val minute: Int,
    private val seconds: Int
) {
    fun now() {
        // call operating system  
    } 
}

// Adding a TimeZone will have a big Ripple Effect
// Changing now() to consider timezone will also bring the effect

Right

// Removed now() since is invalid without context
data class Time(
    private val hour: Int,
    private val minute: Int,
    private val seconds: Int,
    private val timezone: String
)

class RelativeClock(private val timezone: String) {
    fun now() {
        val localSystemTime = this.localSystemTime()
        val localSystemTimezone = this.localSystemTimezone()

        // Make some math translating timezones...

        return Time(..., timezone)
    }

    // ...
}

Conclusion

There are multiple strategies to deal with legacy and coupled systems. We should deal with this problem before it explodes in our hands.

More info

• How to Decouple a Legacy System

Credits

• Code Smell 16 - Ripple Effect by Maxi Contieri