I used to think that individual multilingualism was a blessing, at least for me, until I started recently to work on my Russian. Now I feel that it is a double-edged sword and can also be a curse. My original intention of renewing my intensive study of Russian almost after 20 years was to raise the level of my proficiency in this language to the level of proficiency I have in Yiddish and Esperanto, as I have enough occasions to use it here in Israel. But Russian is so difficult that I have already become rather pessimistic about this possibility. Hebrew, English and Japanese are the three languages I have been using longer and more actively than any other language, so I will not forget them, even if I should not use them for a long time. I have been using Yiddish and Esperanto less long and less actively, so I have some lexical lacunae in my knowledge of these languages, but I will not forget them, either.
Keeping five active languages is not so simple, especially if most of them were acquired in a formal setting and not naturally from childhood in the situation of societal multilingualism. And adding another one to this list becomes more difficult, even exponentially. I feel that I have imposed upon myself the "yoke" of remaining enslaved to languages. Keeping in active memory the same terms of daily and academic life in six languages is a huge waste of what few intellectual resources I have. If I could manage to cover all my daily and academic needs in one or even two languages, as certain people in certain countries do, I could make a better use of the time and energy for more productive intellectual activities instead of constantly "ventilating" these six languages so as not to forget them.
Strangely, I find it easier to memorize abstract difficult words than simple terms for daily life and the physical world, including names of animals and plants. And my memory is still in great confusion about equivalents for the same physical objects in these six languages. I am planning to start compiling an online hexalingual thesaurus for myself in the near future so that my self-imposed enslavement to languages will be more of a blessing than a curse.