Everytime I run an experiment in the lab or look in a telescope.
Even at the individual level your brain is dependent on the witness of the senses, which in turn witness to our nerves, which in turn witness to our brains. Their are many links, each of which could break and make the final witness to our brains false.
Also, when I want to be absolutely sure about what I am seeing, I ask others to look too. I rely on their witness to confirm my own.