Test your assumptions

You can have the most secure architecture in the world, but if you don't test the implementation, you won't realize it when things go wrong.

Modern IT infrastructures change quickly, and assumptions don't age well.

Where do you think your beloved app is the weakest?

Try to break it.

Keep track of the steps you took to test things and see if you can automate them. Then run those on every deploy.

You will be wrong one day. Make sure you find out early.