as janab george w bush said
fool me once, shame on you
fool me twice..aint gonna fool me again..
I like it better than the original saying anyway..
because you dont want to be fooled twice..you may want to give someone a chance or two, in which case you are not being fooled but testing ppl out.
Its the dynamics we see in khandani politics and even work see us giving ppl too many chances, and too afraid to confront or deal with situation. In some cases its worth confronting in other cases its best to just walk away. It depends on the situation and individual etc.