After the code, the second most important product of the developer's work is the documentation.
The entire architecture, from the structure of the network to the interaction of applications with each other, all the technical solutions must be fixed in a place which is easily accessible by the whole team.
Only an amateur developer dares to claim that his code is the documentation. A true professional has an obsessive habit of leaving documentation on everything, not only for his current and future colleagues, but also for themselves from the future.
Documentation should contain not only descriptions of what there is, but also how to use it and in which direction to develop it.
Proofs of concept and small experiments that have been conducted but not continued are also worthy of documentation.
A company without a documentation culture is always one step away from a loss of technical competence and inevitable slowdown or even degradation of internal technical progress.
A company where it is normal to maintain and expand documentation always has a clear picture of all its processes, decisions made and an understanding of how to move forward.
Mentors opinion
I know by experience that it's easier to write a page of code than a page of documentation. You always want it to be smartly written and beautifully designed. And when it doesn't work that well, you want to throw it all away.
But the main point of documentation is not to have a nice design, but to be useful with information that will guarantee to save you and your colleagues a lot of time in the future. With a little practice, writing documentation will become a habit and will get much easier.