Documentation is everything. It’s not just something you do after your project is designed and done. No, it’s something you should be doing from the start of your project. No, it’s not just documenting code. And no, you can’t just have it in your memory, you will forget it eventually. Or you will leave the organization for new challenges and all the knowledge leaves with you.
Documentation is the memory of the organization. There is a vast ocean of tacit knowledge living within its employees that is never written down or documented. And big organizations are siloed, they only remember what their silo must remember. This can be a challenge, especially if there are operations spanning multiple siloes and responsibility is shared.
Employees and their roles are constantly changing and switching between different teams, which really emphasizes the importance of documentation. The developer or the designer from your team might move on next week but the project still has to move on at the same speed, meaning someone has to quickly absorb all the knowledge this person possesses. If that person has documented their work from the start, that process will be much simpler.
Documentation has to be accessible. It has to be somewhere where it can be easily accessed to make it easy enough for people to actually open and read. This could mean having up-to-date wiki pages or having illustrated steps next to an industrial machine. Documentation that is not shared is not read.
Of course, documentation is only as good as its written. Documentation done in haste can actually be a big liability, because the worst thing is when the documentation is wrong. Erroneous documentation (or just badly worded documentation) can focus your mind on the wrong things. And you will spend a lot of time trying to figure it out, just because you had the (reasonable) expectation that the documentation was done by someone who knew what they were doing.
Remember, there will be a time when you will move on from the organization you currently work in. The organization will live on without us and we will too. But both will have great memories of that time, if documented correctly.