I have never agreed with this statement. Scrum is easy. I can explain it in 5 or 6 sentences. If you agree with the basic principles and design decisions, Scrum makes sense and is very easy to follow.
However, most organizations are not structured around these principles. Scrum therefore implies changes in how people work, and those changes are really hard for most organizations:
I think the challenge of doing great things with Scrum is reflected in “the first impediment”: not having a Scrum Team with the skills and authority necessary to be a Scrum team. The PO can’t decide. The Team is not cross functional nor does it own their time or infrastructure. The Scrum Master does not have time or access to management to make improvements happen. Fail before you begin.
If you want to get off to a good start with Scrum in your organization, get your management involved to fix or prevent the first impediment! Get the roles right. I believe if you do that, everything else is much easier.