‘The notions most worth questioning are just those which are most taken for granted.’ 
I’m not sure who said “Truth cannot be told, it can only be found” (or something along those lines), but I believe there’s something very important in this idea.
Each of us must search for our own truth/s. When you find your truth, you cannot impart it to others. You can share your truth in the context of it being your truth, understanding that the person you are sharing it with may enjoy your perspective and gain some insights from it, but in the end must find their own truth for themselves.
If you accept a truth or “The Truth” that someone is trying share with you than you become a sheep. While there’s lots one can learn from those around them, especially those who have searched and thought critically about what is usually taken-for-granted, there’s still a process we each of us are called to do.
I realise some religions call their congregations to be sheep, preaching that it is the sheep who will be rewarded in this life or another. Even some areas of the academy, and in economics and politics (especially in Australia), encourage and reward sheepish behaviour.
The greatest danger of being a sheep is that your shepherd may lead you down the wrong path, maybe off a cliff or to an abattoir… If one doesn’t stop to question where all one’s other sheep-friends are going, and where and why a shepherd is taking them, they leave themselves vulnerable to be used and abused by those in power, whether it is the intention of the shepherd or not.
Not all religions discourage questioning of the doctrinal truths. Some religions teach the opposite. For example check out my post on the Buddhist Kālāma Sutta, the “Charter of Free Inquiry” if you haven’t already.
It is a worthwhile process to question what we are told, questioning what we have not been told, questioning our assumptions, questioning our leaders and teachers, questioning their assumptions, and thinking about how they came to believe what they do.
The questions we ask must consider the most fundamental assumption in our lives, those things that we most take for granted. This means questioning the direction we are going, the implications of our actions, and after careful observation, analyses and foresight, deciding where we want to go and what actions are likely to take us there.
 Alan Watts, The Two Hands of God : The Myths of Polarity (London: Rider, 1978). p. 34. Watts says this is what Whitehead showed us.