How can finding out that a hypothesis is not true be for scientists?

Answer 1

Remember that a hypothesis is a 'good' guess about a question. If a scientist comes up with a hypothesis, she will test it and then see if the testing will say 'yes'. She will then do these many times and if the answer still is 'yes' she will have it published. Many others in the same field will then review that data and they will add to the information or they may not agree.

Answer 2

The key to science is that any scientific theory must be capable of falsification. That is to say, a scientist must be able to come of with a hypothesis based on the current understanding and then design an experiment whose outcome would prove that the hypothesis could not be true (or was extremely unlikely). If that outcome is realised then the hypothesis is rejected and the theory needs to be modified or scrapped. If the outcome is consistent with the theory then it adds moe weight in support of the theory.