Portraits
You can never take a portrait surreptitiously. The person in the picture must be willing to come over, to give themselves to the picture. It's a bond. And if you can't establish that bond, don't bother clicking the shutter. You won't get a photo without that bond. Sometimes I can take a photo in a moment, and sometimes not at all. The subject is somehow on their guard. Don't ask me to explain what it is. Either it is or it isn't.