'Always Give a Reason Why' - How to describe this subject area? I summarise http://rayedwards.com/always-give-a-reason-why/:

In Dr. Robert Cialdini’s book, Influence, he cites a research study showing that simply adding the word “because” to a request multiplies the likelihood of compliance.
Interestingly, the study seems to indicate that the legitimacy of the reasons supplied did not seem as important to the outcome as you might suppose. In fact, it seems hardly necessary to have a real reason at all.
For example, you might ask to cut line at the post office, and be more likely to get a “yes” response from the person in front of you if you simply frame your question by saying something like, “Would it be possible for me to please cut a front of you in line, because I’m really in a hurry.”

I recognise the lack of substantiated evidence in the above quote, but I'm interested in learning about such empirically, scientifically proven behaviour and human psychology (eg through reputable peer-reviewed articles). To clarify, I seek not the hard data itself, but only conclusions and tips supported by credible evidence. I only chanced upon that above link, so to discover more in this area methodically and productively,  what are some key words terming this subject? Where should I start?
I've no training in sciences, so I'd cherish answers and advice written in lay, simple, readable language.
This particular study, sometimes called the "Xerox Experiment", was done by Ellen Langer, who studies "mindfullness", but that may not be what you are looking for.  It is also cited on Wikipedia under Attitude Change - Heuristic Processing:


  For example, people are more likely to grant favors if reasons are
  provided. A study shows that when people said, "Excuse me, I have five
  pages to xerox. May I use the copier?” they received a positive
  response of 60%. The statement, “Excuse me, I have five pages to
  xerox. I am in a rush. May I use the copier?” produced a 95% success
  rate.


It is worth noting however, that a study published in the same year by Stanley Milgram (famous for his obedience experiments in the 60's), cited on Wikipedia under "Breaching Experiments", about people giving up their seats in the subway found a similar success rate when no reason was given, but a significantly lower compliance rate if a trivial reason was provided:


  the second condition, the trivial justification ... a much lower number gave
  up their seats.


A related field that a layman might find more accessible, is called "behavioural economics", and there is also a lot of overlap with "cognitive bias".  Search YouTube for Dan Ariely, you'll learn lots of neat tips and tricks just like this one, backed by peer-reviewed studies, about how easily people can be manipulated.