Falling down in a grocery store only seems trivial or funny if it happens to someone else. The reality is far different. People fall in bars, restaurants and grocery stores everyday. They slip in parking lots on their way into a store. Slipping on something as seemingly harmless as watermelon juice can cause life changing injuries.
To prevent harm, as much as is possible, the law requires that owners and operators of commercial establishments take such reasonable care as is necessary to make sure that people are safe while they are on the premises.
The law does not demand a standard of perfection. Simply falling and being injured in the produce section of the local grocery store does not mean that you are entitled to compensation. The law requires that the people who are responsible for the store have a system of inspection in place, which is functioning at the time, to ensure that the area is clear and safe.
For example, the people who run grocery stores must inspect the floors. They must inspect them in a systematic fashion often enough so that it is reasonable to conclude that if watermelon juice does get on the tile floor, it will be discovered soon enough that it will not present an unreasonable hazard.
If you are hurt and think it might have had something to do with the condition of the premises you should seek an opinion from an experienced lawyer.