I love it when one's privacy is respected. One should be entitled to his or her opinion or whatever he or she deems fit not to tell any other person. The major challenge to respecting the privacy of a loved one is trust.
There are two things involved. If every individual could guard these two things, it would be very easy to respect others privacy.
The first one is trustworthiness. You have to be trustworthy so that people around you will believe you in whatever you say without going the extra mile to find out what they consider the truth. When you are trustworthy, there is no need, for instance, for your wife or husband, if you are married, to intrude on your privacy. When you are trustworthy, it becomes easier for you to trust another person.
Many people do search their partner's or children's phones in an attempt to unravel whatever it is that they are suspecting. I can say that such people have trust issues. However, one thing we should understand is that people who trust you will hardly trust you again when you breach their trust. A husband who decides not to check his wife's phone or vice versa will find it unforgivable if it is later revealed in whatever way that the spouse is involved in infidelity. At that point, he would regret his years of respecting his or her spouse's privacy.
As for me, I learned to trust and be trustworthy as much as I could. No one is perfect, but we can only try to be the best that we can. I respect the privacy of my friends, but when I have to intrude into your privacy for your advantage, I do so.
When I was in university, I had a friend who was hiding his grades from me. We offered the same course together, and when I went to the notice board where the results were pasted to check my results, I realized that his results had been shaded with a pen. I returned to the hostel and informed him of what I noticed, and he was shocked at the development. He later informed me that he had gone to the department to check the copy of the results and that he got an A.
A few days later, another friend who offered the course sent me to check his result for him because he wasn't in town. I went to the notice board and saw that the whole result sheet had been replaced. Heavy downpours had washed them off the board, and they were replaced. It was then that I saw my initial friend's result as F. I was surprised that he could keep such a thing away from me. I initially decided to respect his privacy by not asking him anything regarding the issue, but on a second thought, I felt that keeping silent wouldn't help him either. I called him and politely talked to him. I let him know that failure isn't the end of the world. He should share his problems with me so that we can look for a solution together. My talk was helpful. His attitude toward keeping everything about himself secret changed for the better. He appreciated that act for years.
Another instance in which I can intrude on someone's privacy is if the secret you are keeping is very dangerous to you. Take, for instance, a drug addict trying to do away with drugs. If I see traces of drugs around that can make him derail, I will pick away the drugs.
One thing I don't do is dig into people's privacy. I respect everyone's space, just as I want others to respect my space. This is how I draw the line.
However, I cross the line when doing so to save the person from trouble or to help him achieve his goals. I make sure that I don't dig to get any information that is not freely revealed to me. If, by one way or another, I get to know of it, I will weigh the effects on the person. This will direct me on whether to cross the line to talk to him or not.