Command-Query Violation

SomeClass-bad.cs

class SomeClass{
  private int reason;


  public bool Go(){
    int value = SomeBigCalculation();

    if( value > 5 ){
      this.reason = "Too Big";
      return true;
    }

    return false;
  }
}

SomeClass-good.cs

class SomeClass{
  private int reason;

  public bool IsTooBig(){
    int value = SomeBigCalculation();
    return value > 5;
  }

  public void SetReason(){
    this.reason = "Too Big";
  }
}