Contesting a will can be a long and exhausting process along with an emotional and financial burden for you and your family. In some situations though, it is necessary. Here are some considerations if you're contemplating a will challenge.

When to Contest a Will

Improper Execution - When legal formalities are neglected, then the will may not be valid. This is especially true in Ontario, where strict compliance with the formalities of will execution is required.
Lacking Testamentary Capacity - To make a valid will, the testator must have had the requisite testatmentary capacity. If the testator lacked the mental capacity to draft a will and understand its implications, then the document may be deemed invalid. For example, someone suffering from advanced dementia likely can't execute a valid will.
Exclusions - If a spouse or child is missing from the will, then this may be grounds for a contestation, as there are various legal obligation to ensure dependants are taken care of. These rules can vary quite significantly from province to province.

What to Consider Before Contesting a Will

Personal Toll - The process of contesting a will can be emotionally taxing on the contestor and the others involved in the estate. Since the financial stakes can be high, a will challenge can easily result in an acrimonious dispute between family members and friends.
The Financial Cost - Contesting a will can be expensive and time-consuming, particularly if the dispute goes to trial. If you're thinking of challenging a will, it's important to discuss your case and your options with a lawyer. You need to get a sense of the likelihood of success, the cost of litigation, and the possibility of cost awards. And you need to balance this against the payoff from a successful outcome. A small estate may simply not be worth fighting over.
Other Options - Contesting a will might not be your only option if you have concerns about the validity of an estate planning document. Depending on the situation, it may be possible for the parties to reach an amicable solution without going to court. If the underlying issue is more of a family dispute than a legal one, it may be best to pursue other types of dispute resolution. Litigation is a lot of things, but it's not great therapy.

Contesting a will is a long process and potentially can result in the opposite of what you hoped for. Consider your options, review your case with a lawyer, and decide for yourself if challenging a will is the appropriate action in your circumstances.