Have you ever encountered something like this?
(Note: #r denotes a collapsed region of code)

public class MyBulkyClassThatDoesALot
{
    #r Private fields
    #r Constructor
    #r Another constructor
    #r Public properties
    #r Public methods
    #r Private methods

    #region Validation

    // meanwhile, somewhere on line 20485
    public ValidationResult Validate()
    {
        ValidationResult result;
        CheckThatSomethingHolds(result);
        CheckThatSomethingElseHolds(result);

        if (this.somesituation)
        {
            CheckSituationDependentCondition(result);
            CheckSituationDependentOtherCondition(result);
        }

        ...
        // Somewhere on line 20585
        CheckLastThing(result);
        return result;
    }

    private void CheckThatSomethingHolds(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition X failed"));
        }
    }

    private void CheckThatSomethingElseHolds(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition Y failed"));
        }
    }

    private void CheckSituationDependentCondition(result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition SituationDependent1 failed"));
        }
    }

    // Are you tired of scrolling yet? Good, because this is how whomever reads this code shall feel in real life ;)

    private void CheckSituationDependentOtherCondition(result) { ... snip }

    // A sigh of relief when you reach the last one
    private void CheckLastThing(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition Z failed"));
        }
    }

    #endregion Validation

    // And then, of course, there is a lot of code after this. If you're unlucky, there wasn't even a #region around all the Validation methods and you have to hunt them down one by one because they are scattered through the code.
}

Don’t worry, you’re not the first one to end up with this. Often, it started as a single validation rule that was just implemented directly in the class to be validated. However, there are some things to look out for.