1. Manual testing is slow and costly. Because it is very labor-intensive, it takes
a long time to complete tests. Increasing headcount increases cost.
2. Manual tests don’t scale well. As the complexity of the software increases,
the complexity of the testing problem grows exponentially. This leads to an increase in the total time devoted to testing as well as the total cost of testing.
3. Manual testing is not consistent or repeatable. Variations in how the tests
are performed are inevitable, for various reasons. One tester may approach
and perform a certain test differently from another, resulting in different results
on the same test, because the tests are not being performed identically.
4. Lack of training is a common problem, although not unique to manual
software testing.
5. Testing is difficult to manage. There are more unknowns and greater
uncertainty in testing than in code development. Modern software development
practices are well-structured, but if you don’t have sufficient structure in testing,
it will be difficult to manage.
Source:
Happy About Global Software Test Automation
A Discussion of Software Testing for Executives
By Hung Q. Nguyen, Michael Hackett, Brent K. Whitlock