As anyone who has ever seen a Liberty Mutual commercial knows, we're all only "human" and life is filled with all different kinds of accidents.
There are those times when we are careless and cause injury to ourselves; in that instance, when no one but we ourselves are responsible, there is no lawsuit for one's injuries. For example, there is no one to sue when you knock over your ironing board with a hot iron onto your foot, or when you trip on a toy left in the middle of the floor by your three year old. As another example, if you slip in a puddle of water at a restaurant, but happen to be lucky and do not fall, and are not injured, that also lacks the makings of a lawsuit for personal injury.
They teach us in law school that every "negligence" case must have four elements: (a) a person or entity who owes a legal responsibility to you to not injure you; (b) the person with such responsibility accidentally hurts you anyway; (c) that person's carelessness causes you to suffer injury; and (d) those injuries result in medical expenses, lost wages, pain and suffering, etc.
You must have all four of those elements to bring a lawsuit. In Florida, even if you are partially at fault for causing your own injury, you are still allowed to bring a lawsuit (that is called "comparative" negligence).
At the end of a case that goes all the way to a trial, the jury is asked whether the person or entity who injured you was responsible for the injury, whether that person's carelessness caused you to suffer damages, and asks the jury to determine the amount of your damages. In the event that you have some responsibility for your own injuries (for example, after being broadsided when making a left turn, juries often find both the "broadsiding" vehicle and the turning vehicle partially responsible for causing the accident) the judge will then reduce the damages that the jury awards you by the percentage that the jury says you were responsible for causing your own injury.
The bottom line is that sometimes injuries do not appear immediately, and sometimes there are questions about who or what entities might be legally responsible for causing damages to an injured victim.
Because there are so many nuances in negligence law, you should always contact a lawyer (almost all personal injury lawyers charge nothing for a consultation to determine, at least preliminarily, whether you have a case) to see whether you do indeed have a negligence case or not. The legal analysis of these issues and the willingness to pursue a fight for justice for one injured victim–even without asking for any fees or expenses until that victim recovers money from the negligent party–is the reason why people hire personal injury lawyers in the first place.