Knowledge is dangerous when it is broad, but superficial and disconnected from a commensurate wisdom and capacity. A 5 year old may well understand what is required at a basic user level to drive a car, but he does not have the wisdom, maturity, and physical capacity to do it well or safely.
Knowledge is also dangerous when we have knowledge far beyond our need and station in life. This can make for great unhappiness, especially the unhappiness associated with envy. In our day and age we tend to evaluate all things in terms of the pleasure we receive from it. And idle curiosity can be followed to just as destructive effect as an unregulated appetite for food. This is especially so in spiritual matters. Every monastic and aescetical discipline holds knowledge that it does not
share with novices, even if the novices are aware of the existence of such knowledge. They are not encouraged to seek it out before the elder members of the community deem them ready to receive and internalize such knowledge. They know from long experience it can very dangerous if just ladled out willy nilly. In the Eastern Orthodox Tradition there is a book written by and for monastics. It is a compilation of wisdom and teachings from saints and holy ascetics going back over 1000 years. It is called the Philokalia, The Love of Beauty, and it is about the practice of the Jesus Prayer. There are some parts deemed suitable for novices, and others that are forbidden until one is a
deeply experienced, even accomplished monastic of more than 40 years of age. Those parts can only be properly understood and applied by those who have attained to a similar state of spiritual life. It's like mathematics, the one struggling to master addition and subtraction has no time or need for calculus and string theory, that is a recipe for despair. Rather you want the novice to move from basic math to simple algebra, then a gentle introduction to geometry and trig and basic physics and then maybe calculus and what lies beyond that.
Too much knowledge acquired too easily, too soon, too cavalierly is a destructive burden and not useful as an intellectual or spiritual (though this is a different sort of gnosis) tool it was meant to be.