The purpose of hypothesis testing is to test whether the null hypothesis (there is no difference, no effect) can be rejected or approved.
If the null hypothesis is rejected, then the research hypothesis can be accepted. If the null hypothesis is accepted, then the research hypothesis is rejected.
to decide between two explanations:
I.The difference between the sample and the population can be explained by sampling error (there does not appear to be a treatment effect)
II.The difference between the sample and the population is too large to be explained by sampling error (there does appear to be a treatment effect).