In general, there are four different outcomes that are possible when testing a hypothesis:
Your hypothesis is true and you determine that it is true.
Your hypothesis is false but you determine that it is true.
Your hypothesis is true but you determine that it is false.
Your hypothesis is false and you determine that it is false.
The first and last cases are "good" since you have accurately determined the truth of the hypothesis. The second and third are however bad since you either believe something that is not true or you don’t believe something that is true. We would like to minimize the likelihood of allowing these last two possibilities.