I know it looks bad but he/she had good intentions. It didn't turn out how anybody would have hoped, but at least her/his intentions were good. It is not so much of a saying here (USA) as it might be an explanation for something that did not turn out well.

1) Be kind to everyone because you do not know what each person is going through. 2) Don't judge a man unless you have walked a mile in his shoes. These are two that come to mind. Terasee

"...but his/her heart was in the right place." That's another possibility.

I found the source, and the source has translation to English, and what the translation says is: Judge everyone favorably, the source is here http://www.shechem.org/torah/avot.html chapter 1:6 will I be understand if I will say 'judge me favorably' or 'he judge him favorably' if not, what do I have to use in everyday conversation insteed?