Like a knife that needs sharpening, so does the brain. A sharp knife is a good weapon for cutting materials. Blunt blades will only hinder the work so that the work becomes ineffective and takes longer. To keep the sharpness it will need to be done grinding so that all that will be cut to be effective.
If we rarely to train it. It is very hard if we have to think hard to get an idea if we had never thought about it specifically. If the blade should be kept sharp, then our brain must also be trained regularly in order to develop like a sharp knife. Train the brain can be done with critical thinking on every thing, learn a variety of science, and routine in making creations. Brain training must be done firmly against laziness. So, we have to ensure our productivity every day. We can also use friends or communities to remind each other to mutually motivate to do things that are productive.