You know what people think about politicians. It is said that they constantly lie, they do things wrong, they spend our tax money awfully... In extremely cases, when things are really bad, people also say it's their fault or even insult them (yes, maybe some of them are stupid, but that's besides politics)
What if -most of them- didn't lie to us all the time, what if they actually wanted the best for our countries? Eventhough their best guess isn't actually what we need.
Do you really think someone elected would, in any case, attempt to harm their electors or do something clearly bad for their country for no reason? Why would they? Unless they are just stupid, but only some of them are.
Maybe I'm wrong but consider the following: Imagine you, the unselfish average smart citizen and a "good person", are a politician. Wouldn't you try your best to give your electors what you promised? Wouldn't you be honest with them and stay away from troublesome issues like corruption or any kind of fraud?
And that's for good people. Okay, not everyone is a "good person". Then let's imagine you are the worst person ever. You are selfish, you don't mind others and you only want us citizens to make cash and enjoy power. In that case, my take is the same.
You would try your best to give what you promised and make the country (or the city or whatever) develop and grow correctly, even if it's just to keep people happy and be re-elected. You would also stay away from trouble so your image doesn't get harmed and you can continue enjoying your charge.
So if you don't achieve what you thought you could, or what you told people you would achieve, I'm sure it's not because you arbitrarily promised random things so you could be elected, but because something unexpected happened or you were short of cash and therefore you had to make some sacrifices or change your mind in some way.
Of course there are exceptions, corruption and obvious lies happen. But let's suppose those who act that way -and their parties- are punished for it later in the polls and/or in jail.