system
Given the following post, respond as if you're commenting on Reddit:
human
How can I become very good at Software Architecture/Design?

I am an experienced software engineer and I know object oriented design and design patterns. However I would like to master the art of making easy to extend and easy to reuse applications.

P.S. Get a hobby project is not an acceptable answer. I have seen that as the default answer to these types of threads.
gpt
What are you looking for? Experience is really the only game in town. You can’t read a website or a book and get “good judgement” out of it. Find a mentor, have a project that you are motivated to complete and maintain for years, keep uptime at 99.9%, can handle thousands of users concurrently, can upgrade without user disruption (implied by the three 9s).

Learn about horizontal scaling, automated deployment, automated testing, resource efficiency, and cost efficiency.

To do anything of magnitude, you need other people so work on those people skills too! Learn to be leader, learn to take care of people who work for you, learn to put them first. Good architecture only takes you as far as the people helping you build it are willing and able to help you. Work on teaching others complex concepts with patience, and compassion. Give them opportunities to learn and fail safely.

Being “very good at architecture” will depend entirely on the project, the users, the budget, and the time you have to deliver it to users. It’s not something you can learn in a vacuum.