What is the difference between observational research and casual people watching?

The act of observational research is very different to that of casually watching people undertake an activity. Take these two scenariOS for example.

*You are studying to become a "Bio-chemist" and your lecturer is teaching you how to mix chemicals in which you need to write an assignment on the chemical reactions* This is observational research.

Casually watching is like settling down at night to watch your favourite television show.