Having been on the other side of this countless times, those small moments of generosity and openness from locals can literally transform your perceptions of the world. We are all ambassadors.

Be nice to tourists

Eating cereals is a subtle interaction of milkiness, crunchiness and time spent soaking. Hat tip.

When combining cereals, layer milk-resistant cereals at the bottom

Classic rule of thumb from Jakob Nielsen. Probably the most useful corollary is if you can afford 15 tests, tests 5 users 3 times each and iterate the design in between.

5 user tests finds 85% problems