An interesting question.

If a dictator fell during his (not many female dictators), was because their time was up(historical dialectic); not they did something different or showed weakness. Total ignorance and absolute confidence are the primary characteristics, hence you can't accuse them of following a policy which they don't believe in. 

Dictators thinks there is no end to their their rule and they are invincible. If they know end is inevitable, they would temper their behavior.

Try to be a dictator for a day. Since you know there is no tomorrow for you on the thrown, you behave to save yourself . 

Dear Sir --- The very RISE and FALL is a common theory of everything so  no matter either human or dinosaur or dictator all have a rise then sure there is a fall -- this is the very LAW OF NATURE and one who respects will see and seek the fall in peace and with peace. Thanks

@George Stoica: Sir King Ashoka. After the Kalinga Battle , he left the path of violence and accepted Buddhism.

A dictator is so consumed in his own greatness that he tends to preclude any criticism. His "greatness" is ever fueled by sycophants who do not want to make him realize his mistakes. And fortunately most of them are not organisation man, who will never let professionals work freely but engage only family members and trusted friends from whom he will receive only praises and not suggestions. The reasons of his rise are also the reasons of his fall.  

Besides, even if the dictator eventually learns the trick of his trade, it becomes inevitable for him to carry on with the existing system. A slight slip may result in lifelong jail, exile or death and not just the requirement to sit in the opposition bench only. Stakes are extreme. Change of policies even by Ashoka led to decline of his empire.   

I think, they didn't read history, and if they did, they didn't understand and take wisdom from others. And sometimes they said to themselves "We are not like X (dictator), our case is different".