 Welcome to this chapter of the Open for Inside course, where we work on finding out how to make a good experiment. More specifically, we will address two areas. Why is observation alone often not enough? Why do we need experiments in the first place? And given that they're necessary, how do we make a good experiment? Although it's already a good start to observe the world when you try to understand how things work, we will see that we can run into trouble pretty quickly when relying on observation alone. We will see a few examples of what the source of these troubles is and how they may mislead us when we rely only on observing the world. After that, we will try to understand why it's necessary to get our hands dirty and create experiments to gain better insights. We will find out about the rationale of experiments, see a few examples from different disciplines, and then do some exercises to make our own experiments happen. The latter part, especially, will be very hands-on.