There is a nuance here -- magicians are possessive of someone else taking credit for their idea and do not appreciate someone selling it as their own. Sort of

There is a nuance here -- magicians are possessive of someone else taking credit for their idea and do not appreciate someone selling it as their own. Sort of like the way the BSD license works. However if credit is given and the new effect is sufficiently unique/innovative, then no objection is reasonably made.