A more useful way to think about testing is as a sequence of interactions interspersed with evaluations. Some of those interactions are predictable, and some of them can be specified in purely objective terms. However, many others are complex, ambiguous, and volatile. Although it is often useful to conceptualize a general sequence of actions that comprise a given test, if we try to reduce testing to a rote series of actions the result will be a narrow and shallow set of tests.

Manual testing, on the other hand, is a process that adapts easily to change and can cope with complexity. Humans are able to detect hundreds of problem patterns, in a glance, an instantly distinguish them from harmless anomalies. Humans may not even be aware of all the evaluation that they are doing, but in a mere "sequence of actions" every evaluation must be explicitly planned. Testing may seem like just a set of actions, but good testing is an interactive cognitive process. That's why automation is best applied only to a narrow spectrum of testing, not to the majority of the test process. If you set out to automate all the necessary test execution, you'll probably spend a lot of money and time creating relatively weak tests that ignore many interesting bugs, and find many "problems" that turn out to be merely unanticipated correct behavior.