The main motive of the QA person should be "How to break into the system". This statement keeps on driving me and helps in delivering the application as per requirement specifications.
What is actually breaking into the system ? - According to me this actually accessing or using the application components by not following the usual way. For Eg. An application has been developed which has a log-in id which accepts only alphabets. So my aim would be to get into this application by entering combination of alphabets and other characters into the log-in field.
The other thing which can be driving force is Patience. A Quality Analyst has to be very patient in understanding the Application flow and Usability. The better is the understanding the better the application is developed in the right direction with help of QA.