In the law, there is a tendency to use big words. Even if the words themselves are small, legal professionals often use words that are difficult to understand. Such is the case with “burden of proof.” It means, simply, “who has to prove what and by what standard—or with how much evidence must something be proven.”
Interestingly, most people are aware of this principle from other aspects of their lives. For example, in the NFL a coach who believes the referees made a wrong call may initiate a review of the referees' decision by throwing a red flag on the field and initiating a “challenge” to the call. The referees will review the instant replay video. The ruling is overturned only if the referees see “clear and obvious” evidence that the call on the field was wrong. In the NFL, the coach seeking to overturn a call has the “burden of proof” and the standard by which it must be proven is “clear and obvious.” This is a pretty high standard—just ask the coach on the losing end of a challenge.
So it is in the criminal realm. We have all seen on television the burden of proof that a prosecutor must meet in order to convict the accused person. The prosecutor must show “beyond a reasonable doubt” that the accused committed the offense. This is also the standard in criminal cases in the state of Washington and Oregon. The prosecutor must prove that accused committed the acts he or she is accused of committing and the evidence must almost all weigh in favor the prosecution's evidence. If there is a reasonable doubt, the accused must be acquitted because the prosecutor did not meet his or her “burden of proof.” It's important to note that in criminal cases, while the prosecutor has the burden of proof on the charges brought, the accused may also have the burden of proof to establish certain defenses—such as self-defense. The accused does not have to “prove” his or her innocence. That's not the accused's burden to prove. The prosecutor must prove the accused's guilt.
In civil cases, like claims for personal injuries, the burden of proof rests with the injured party to prove all of the damages caused by the incident complained of. For example, in a car crash case, the injured person must prove that the collision occurred, that the defendant is at fault for that collision, that the injuries he or she suffered were caused by the collision, and that the treatment received for those injuries were reasonable, necessary, and related to the collision. Importantly however, the standard is MUCH less in a civil case than it is in a criminal case. As discussed above, the standard is “beyond a reasonable doubt”, that's a very high standard. Civil cases have a standard that is much less rigorous. A civil plaintiff must only prove his or her case by a “preponderance of the evidence.” Essentially, a 51% margin—more likely than not—standard. In other words, are the scales of justice tipped, ever so slightly, in the injured party's favor? If so, the injured party has met its burden.
In the end, there are many exceptions and caveats to the general rules outlined in this brief post. But generally speaking, in your civil case, you (or your attorney) will have the burden to prove that you were injured and to prove the extent of your injuries. How that burden applies to each case and the effect it has on a unique situation depends on too many variables to possibly list here. If you have questions or concerns, it might be best to consult with an attorney directly.