Every hexagram has six lines, read from the bottom up, and the first line is the ground floor. In the picture Human Design uses, it is the foundation the whole house stands on, and nothing above it holds unless this level is solid. That is why the first line's insecurity is not a flaw. It is the pressure that makes it study until the ground is firm.
The Role
First lines sit in the lower trigram, the personal half of the hexagram, and their process is inward. They are not trying to reach anyone. They are trying to understand, and they do it by watching how things behave, including how people behave. When a first line feels unsure it blends in, showing you what it thinks you need to see while it works out what is really going on. Once it has its answer it relaxes, and often becomes the person others come to for the answer.
In Your Profile
If the first number of your Profile is 1, this investigating is conscious: you know you need to research before you commit, and you can feel the anxiety when you are asked to act without enough information. If the second number is 1, the same need runs in the body without your noticing, and you may only see it in how uncomfortable you get in unfamiliar territory. Line 1 appears in the 1/3 and 1/4 Profiles on the conscious side and in the 4/1 and 5/1 Profiles where the first line is unconscious.
Living It Well
The not-self version of a first line feels inferior, usually because it never gave itself the focused time it needed to build its foundation and has been acting on borrowed certainty ever since. The correction is permission. Study one thing at a time, go as deep as you need, and let your Strategy and Authority choose which investigations are yours. A first line with a real foundation is the steadiest presence in any room, and its knowledge is the base everyone else builds on.