Hadiths of the Imams
If an individual’s good deed turns them pleased and bad deed turns them upset, they are certainly a believer.
The concept’ faithful’ doesn’t mean’ infallible’. The infallible never ever does wrong, but a faithful may slip somewhere and does something wrong.
The difference between a faithful and others is that, the faithful never gets happy for the wrong they did, even if all admire them. Likewise, they never get sad and regretful for the good deed they did, while all blame them.