In British Columbia (any other jurisdictions may have different rules), and with several exceptions, you must start your lawsuit within two years after you discover that you may have a lawsuit.
There are several conditions and exceptions. For example, there may be some debate as to the date when a plaintiff ought reasonably to have known that the plaintiff had a claim. This is important. The date on which the time within which the plaintiff must start the lawsuit starts on that date (we call this the "limitation period").
The type of lawsuit also changes the time within which plaintiffs must bring claims. Sexual assault claims, claims to enforce secured property rights, claims involving land, and other claims are not governed by the 2-year rule. Some types of claims, such as claims involving fraud, have special rules governing when the limitations period starts to run.
Lastly, there is a rule called the "Ultimate Limitations Period". That is, no lawsuit can be brought 15 years after the date of the event that created the right to sue - which is itself subject to some definitions and conditions.
This is a complex area of law. A good guideline is that if you are thinking about suing someone for something that happened over two years ago, then get some legal advice immediately to find out if your claim can still advance. Depending on the type of case and the circumstances in which you discovered your claim, you may still have a viable claim that has not expired.