Nobody knows everything, let alone parents. Parents are there to support you and have give you advice based on experience that they have had when they were in your age or shoes. Parents may know a lot more than you, but definitely don't know everything about everything. Some parents may think they know everything, but they themselves need to read this.
Being a parent myself, I may want to think that I know everything, but it the end, no one really knows everything. Sometimes to a child it may seem like parents know everything about everything as well as see everything, but this is not true. The mere fact that a parent was once their child's age gives them insights on the outcome of many childhood ventures, but it is far from knowing everything. Regardless of not knowing everything, the wise parent will know where to find the answer to everything!