Upon analysis of the results, a hypothesis can be rejected or modified, but it can never be proven to be correct 100 percent of the time. For example, relativity has been tested many times, so it is generally accepted as true, but there could be an instance, which has not been encountered, where it is not true.

Why can a hypothesis never be proven?

In science, a hypothesis is an educated guess that can be tested with observations and falsified if it really is false. You cannot prove conclusively that most hypotheses are true because it's generally impossible to examine all possible cases for exceptions that would disprove them.

Can a hypothesis be proved and disproved?

This is why hypothesis testing on samples can never verify (or disprove) a hypothesis with certainty (i.e. probability in decimal notation = 1) and can only say that a hypothesis has a certain probability to be true or false.