Security comes, not from having certainty, but from being comfortable with uncertainty.
Watch most babies, and you will see that unfamiliar situations either fascinate or disturb. It depends on the context. The sudden appearance of a new toy can cause a sudden flood of tears, as though newness were a flood of germs coming into the mental immune system. Equally, at other times, perhaps when introduced by a familiar parental voice, the new toy can be an object of curiosity.
It all depends on whether there is a firm base from which to explore. Neither reaction is right or wrong (we need both rejection and acceptance in our childhood armoury). But, just as a vehicle needs clean instruments with good calibration to run itself in a stable way, so a child needs a healthy set of perception tools, with a reasonable range of acceptable signals, to interact with the world in a productive, learning manner.
When we are adults, we can then learn to modify those internal tools in interesting ways. We may choose, for instance, to increase the range of perceptions we find acceptable… in essence, to become more tolerant. Greater tolerance in a person takes great managing: you need to be able to witness stronger experiences without meltdowns; and you need to be able to understand a wider range of scenarios without closing down.
As you get older, you have increased chances to explore what it is to be a unique being, with a unique set of reading tools, faced with a big and varied book called the universe. You can learn to be comfortable with uncertainty. With that ability, you can face a wider range of people, things and experiences with curiosity and wisdom. You can learn to be more compassionate, because you have wider arms with which to hug a wider range of beings.
As I say, security comes, not from having certainty, but from being comfortable with uncertainty. The best relationships, jobs, activities, experiences, and days, perhaps come from moments when you allow your eyes to be open, and your face to smile, despite your unsureness as to whether things will turn out OK.