Regarding Software Engineering, there are several obstacles for Extreme Programming, one of them is reluctant ideas. Not to accepting certain kind of idea.
What is the exact meaning of the term "reluctant ideas"
Well.... asking to explain one aspect of XP without having to explain the rest is kind of difficult. Therefor I would like to start with a short reference about some core parts of XP. XP carries values, here to mention are communication, feedback, and courage. If you are communicating with others from your team and you'r all suggesting solutions (Feedback)... especially if your know-how levels differ ... you sometimes have a situation where a certain "idea"/"solution" for the xyz-problem is based on false assumptions or based on missing know-how.
Those who miss the know-how to see another solution will always come back to the xyz-solution for the xyz-problem. Those "ideas" are called "reluctant". If you look up the term all by itself, you get some definitions:
relecutant adjective 1. unwilling; disinclined: a reluctant candidate. 2. struggling in opposition.
Can be confused: 1. reluctant, reticent; 2. reticent, reluctant.
Synonyms 1. Reluctant, loath, averse describe disinclination toward something. Reluctant implies some sort of mental struggle, as between disinclination and sense of duty: reluctant to expel students. Loath describes extreme disinclination: loath to part from a friend. Averse, used with to and a noun or a gerund, describes a long-held dislike or unwillingness, though not a particularly strong feeling: averse to an idea; averse to getting up early.
From my point of view the "reluctant ideas" are those who are more like a tradition in the sense of "We have always done it like that" than based on experience or know-how. It takes courage on all sides to identify and to get rid off "reluctant ideas".
One example that shoots to my head right now:
(xyz-solution for xyz-problem, but obviously a bit confused)
The "reluctant idea" would be that you are faster (e.g. better coder) by circumventing a VCS. People who never ever used a VCS will often come up with this idea, where as those who use a VCS on a daily basis know (know-how) why using a VCS is the way to go.
XP or eXtreme Programming, like I said in the beginning, carries values. See: http://www.extremeprogramming.org/values.html
If you take these values seriously your duty is to help yourself and others in your team to battle reluctant ideas. And that is most definitively an obstacle :-).