How much time does it take us to learn a certain rule, a law or a fact? And how often we would forget it? One would find an excuse for unusual forgetfulness in the too much terminology or the apparent complexity of such fast forgettable rule or topic. Here, I would try to answer this question: You have not learnt it unless…?
As a constant provision for those who wish to learn many things, as many as they could, is that one cannot and should not learn everything. From the good things, that are apparently beneficial, e.g. sports, languages, manual work, etc., one can choose things that suit his/her learning abilities. On the other hand, one should avoid every bad thing, e.g. saying bad words, telling lies, etc., that apparently would harm rather than benefit.
1- You have not learned it unless you have a successful model.
E.g. there are many attempts to have a model for the structure of the atom; Thomson, Rutherford, Bohr, Schrödinger, .. So the model shaping is important.
2- You have not learned it unless you say it mathematically.
E.g. Mendel could express mathematically the hereditary process for the first time in human history in the garden peas. Mendel’s laws, thence, opened the door to Genetics and Molecular Biology.
3- You have not learned it unless you know its zero and its maximum.
E.g. the different scales for measuring temperature depend on defining a zero point (melting of ice is the 0°C) and a maximum point (boiling of water at 1atm is the 100°C). The absolute temperature scale (Kelvin, K) resides on values that can be extrapolated in the gas laws; 0°C = 273K, or 0K = -273°C.
4- You have not learned it unless you have a scale.
E.g. a famous statement by Niels Bohr (as far as I could remember): “Everything that can be measured is present” or “Everything that is present can be measured”.
5- You have not learned it unless you are aware of its reverse.
Obviously, we would not learn about light in the absence of the darkness.
6- You have not learned it unless you see it.
E.g. the dispersion of white light into its seven colors by a prism is a striking experiment for this fact.
7- You have not learned it unless you make it yourself.
E.g. the art of paper folding, Origami, is very difficult to learn through watching. Step by step self-making is much more feasible.
8- You have not learned it unless you pass it out.
E.g. some knowledge is made much easy to learn and remember by passing it out, e.g. language grammar.
9- You have not learned it unless you see it from above.
Human moral and ethical faults or defects are not completely overcome unless one could avoid and forgive them as appropriate.
10- You have not learned it unless you think you should learn it.