How to make unchecked checkbox sticky

I need some help with my checkbox.

As of now I am able to check my checkbox, save and it will stay saved. But when I leave my checkbox empty and click save again, the checkbox is checked again. How do I fix this?

This is my code:

 <div class="form-group">
                        <label>
                            Not sure about my departure date (select only if there is no date!) :
                            <input type="checkbox" name="not_sure" value="1" @if(old('not_sure', $currentDeparture->departure_notsure) == 1) checked @endif>
                        </label>
                    </div>