Unacceptable flight time changes

Today I received a SMS from Mango's schedule team advising me that my flight for tomorrow would only take off 40 minutes after it was scheduled to leave. This is now the third or fourth time that Mango has changed a flight time spontaneously and without any reasonable notice. If I'm flying at night, this change in schedule is going to cause a serious issue with my travel plans. If I wanted to fly later, surely I would have booked a different time. How does this airline assume that their customers will be okay with this? And do they not realise that a change in flight will cause a domino effect on people's schedules? Or perhaps it is a mere disregard for this inconvenience, in which case the airline will not be my, or others', first choice for flying.