Abstract: I am a dedicated user of quantum mechanics. I feel, however, that we restrict ourselves too much about quantum mechanics. For example, yes we know that Bell's inequality is violated. But is that all? Why the value is neither 2 nor 4 but 2.8284...? We do not know the answer yet but it can be a rewarding question. In this example we are encouraged to go beyond quantum mechanics. Next, it is said that we cannot look inside an interferometer without disturbing interference. Using weak measurement, however, we can obtain an average of an observable, and sometimes, such average value is enough and has interesting information. In this example, we are encouraged to reconsider so called "principle" using quantum mechanics itself.