This is a very deep but very profound aspect of the Buddha’s teaching, to be open to uncertainty, to be open to the unexpected, because this is the real nature of life. So realising that this is the real nature of life we cease trying to control the environment in particular ways. Of course it can give a sense of security when you think that everything is under control and there is no problem, but this kind of security is a very fragile, false kind of security.
According to the Buddha’s teaching, real security comes when we can be open to insecurity. When we are open to insecurity, then whatever happens, to a great extent you’ll not be surprised and then you can see that as an object of meditation, you can make an effort to learn from that. Internally we are allowing anything to arise, any unexpected things to arise, such as an emotion, a sensation, or a thought. So whatever arises we learn to see them, as the Buddha said, just as they are.