Our brain is capable of making many connections when we learn and perform. It makes these connections by exchanging chemical messages at the most basic level of individual neurons, that promote the firing of the same neurons in response to the same experiences. The general expression of this is "the neurons that fire together, wire together".
The consequence of this is that maps of learning and performance are reinforced with recall and practise. Those paths that are little used, exchange less of the reinforcing chemicals, and stop firing together. This means that our memories fade with time if we do not use them, and any collection of them, starts breaking down with time as other events compete or steal away these associations.
The expression "use it or lose it" is true. However, most of these patterns in our memories are not lost completely, they are just taken over by other more frequently visited patterns in the brain. Our brain maps are ever expanding or contracting depending on how we use them.
The consequences of this are many, but in terms of initial instruction, the core things that you want to perform, should be learned first, and practised often. The trick is determining exactly what the core path should be for the particular task at hand.