Are inhibitory synapses the cause of not doing something? Imagine you are driving your car, in front of you, you see a wall. What prevents us from driving against the wall? Is this accomplished by the brain having inhibitory synapses established here?
Inhibitory synapses allows one brain region to suppress activity in another. Since the car is in motion per the laws of motion and momentum, it would be incorrect to say that suppressing one brain region would cause the car to stop moving toward the wall. The closest thing would be if those inhibitory synapses caused one part of your brain to inhibit the part that causes your foot to press the accelerator pedal. For example, dopaminergic neural processes from the basal ganglia (particularly the substantia nigra) indeed suppress motor impulse indirectly (see here and here). However, more activity than simply releasing the pedal is required in most cases to avoid hitting something. In short, you most certainly need both inhibitory and excitatory synapses to help you avoid running into something on the road or on your path as you walk. These functions are probably very complex, involving a great many of both types of synapses in several brain regions.

It is important to remember that many if not most neural circuits are primarily for very specific actions in the body or mind. Most "actions" in the common sense that a person can undertake are the result of a great many action potentials in the brain. Perhaps in some very small (such as microscopic) creatures, a single action potential is needed to initiate an activity such as feeding, but larger creatures with bigger brains have so many neural pathways that most observable actions of the animal require many internal actions of the processing system.