When we learn new words of a foreign language, we forget them with time if we don't use them often.
To avoid this, we have two options: to live in the country of the language we are learning, or study every day the new words we learn to not forget them. The first option is clearly not affordable for everybody, and the second one is not a good idea because we would not know what words really need our attention.
If neither of the two options seems to be a good alternative, what do we do?