Estates and Elder Law in Canada, posted an article about why the drafting of wills is best left to lawyers. The logic behind this is simple: the law is complicated and even the smallest of language mistakes can lead to an outcome not contemplated or wanted by the testator. Click here to read Mr. Staples' article.
In the article, Mr. Staples discusses the Ontario case of Budai v. Milton, in which the testator had his will written by a retired financial planner. The will was not straightforward, in that it contained some paragraphs drafted completely by the financial planner (as opposed to being standard or boilerplate clauses). Unfortunately, drafting of legal documents is not something that non-lawyers should do. The court struck down a clause that said a beneficiary could not challenge the will in any way.
If your will requires specialized drafting because you have a very specific wish or unusual request, make sure that it's drafted by an experienced wills lawyer.