well, in some cases it's true... it's a mental disorder... but in some cases it's not... Just like in BDSM.... I'm an alternative lifestyle consultant who is also work as Professional Dominatrix... In our community there is a masochist who enjoys receiving pain and have pleasures in it... A masochist needs a sadist who also enjoys giving pain...
There is a limitation on sadist power thru written contract/agreement were both individuals agreed to it...