Context: children aged 3 and up are inquisitive. This is usually fun - but sometimes, you get tired of the unending why game, or the 'why' is just too complex to explain, or you are embarrassed by a question that touches 'adult' topics, or you just don't want to answer.
Problem: you don't know how to answer your child's question (or don't want to). Like a lot of parents, you are tempted to lie, or evade the question.
Forces: as a parent, you are the authoritative source of information for everything the child doesn't find out by herself. Your child trusts you absolutely; undermining that trust deprives your child.
Solution: answer truthfully, even if you don't answer the question. If you don't want to answer, for whatever reason, say so; if you don't know, say so; and if you think the answer is too complex, say the simplest thing that could possibly answer the question.
Resulting context: trust is preserved, and in addition your child learns that you are not always inclined to answer questions, which will incite her to find things out by herself.
On the other hand, you'll also encourage her to ask more questions. ;)
See also DoNotLie
My father used to make me sit by his side when I asked a question, as he proceeded to look up the subject matter that I had just asked about in our Encyclopedia. I soon picked up the habit of looking it up myself. This doesn't work all the time, but at least it instilled a life long habit of self-education and research.
Part of a potential PartnerPatternsLanguage