A great teacher tought me that a workable application's first criteria to success is to work correctly what it suppose to work first then others terms like velidation and verification comes up. For a tester, I will say he/she need to know and practice exploratory testing first to become a responsible tester other things comes after, doen't matter whatever methodology you are working.
Exploratory testing is importent because,
- You will learn as you use
- Notice very silly mistakes in application
- You will learn to fit in developers shoes
- You will learn how users will use so you will give good feedback about improving the state of the application
And there is much much more, still I am EXPLORING ;)
