> How is it possible that a serious study is harder to replicate than it is to do originally.

They aren't. GP was on point until that last sentence. Just pretend that wasn't there. It's pretty much always much easier to do something when all the key details have been figured out for you in advance.

There is some difficulty if something doesn't work to distinguish user error from ambiguity of original publication from outright fraud. That can be daunting. But the vast majority of the time it isn't fraud and simply emailing the original author will get you on track. Most authors are overjoyed to learn about someone using their work. If you want to be cynical about it, how else would you get your citation count up?