A good tester knows that he has to pay attention to detail. Coding is detailed work and a small mishap or oversight can disrupt the entire program. Hence, testers need to be vigilant when going through their data in order to progress through the program. He needs to be vigilant when executing unit tests against code that he has written.
This ensures that the system is performing at its best and all possible bugs and flaws have been eliminated efficiently. This is a valuable asset for the customer and needs proper attention. The detail ensures that the entire code was thoroughly searched for flaws to make sure there are no problems.