We have seen in the previous sections how the commits are linked to each other by a parent-and-son relationship: each commit contains a reference to the previous commit.

This means that, for example, to navigate within a repository I cannot start from the first commit and try to go to the next, because a commit has no reference to who comes next, but to who comes first. By staying in our arboreal metaphor, this means that our tree is only navigable from leaves, from the extreme top of a branch, and then down to root-commit.

So, branches are nothing but labels that are on the tip commit, the last one. This commit, our leaf, must always be identified by a label so that its ancestors commits can be reached while browsing within a repository. Otherwise, we should remember for every branch of our repository the hash code of the tip commit, and you can imagine how easy it would be for humans.