The Simcha of Shavuos is for officially having accepted the Torah, not necessarily for actually being M'kayem the Torah. We can suggest that the Yom Tov of Simchas Torah is a celebration for finishing the entire Chumash, but Shavuos celebrates the mere acceptance of, and desiring the Torah. When the Yidden decided to do the Korban Pesach, it says: וּשֲׂﬠַיַּו וּכְלֵיַּו בא יב כח they “went” and they “did”. Rashi explains that although they hadn't yet done anything, since they were M'kabel to do it, it is as if they actually did it.
The Medrash says that the extra word: הָנְכַלֵתַּוםֶהיֵתְּשׁ רות א יט teaches us: ֵכּ ָוי ֶשׁ ן ָנ ְת ָנ ַד ה ֲﬠ ָתּהּ ְל ִה ְת ַג ֵי ִה רי ְשָׁו ַה ה ָכּתוּ ְל ב ָנ ָﬠ ִמי רות רבה ג ה as soon as Rus just decided to be M'gayer, she became equal to one of the greatest women in Jewish history, Naomi. A person has no idea of the Chashivus of your wanting to improve or deciding to improve yourself! This is why there is so much unnecessary pain going on in so many of us.
When we worship humans who only care about success (even in Ruchaniyus) then we are in trouble. Similarly, we have: דִוָדְל תִיַבַּה תַכֻּנֲח ריִשׁ רוֹמְזִמ תהלים ל א Dovid is given credit for building the Bais Hamikdash, even though he never did, because he tried and wanted to do!
The more Simcha you have with your own Torah and Mitzvos, the more you are on the Derech HaYashar. And the more internal or external kvetching and dissatisfaction that you carry around, the more you are away from the Derech HaTorah, Rachmana Litzlan.
However, in a Dor like ours, I would be: רֶשׁוֹי ץיִלֵמ stick up and be Dan L'kaf Zechus, and say Aderaba! A person who serves Hashem with all kinds of worry and pain and Atzvus (sadness) and complaints, may be even greater, since: אָרְגַא אָרֲעַצ םוּפְל אבות ה כב the reward increases according to your effort. But of course, Le'chatchila we aim for more and more Simcha; especially Sameach B'chelko and Shaar HaBitachon.
Remember this Shavuos to respect every tiny Ratzon, and the faintest of your holy wishes to improve yourself as a mini form of Kabala (accepting on yourself to do) since this is the most you can do for the moment. And the Zechus of appreciating your even inferior Avodas Hashem, will help you grow more and more, with Hashem’s help, since Hashem sees that you are satisfied with what you have, albeit as tiny and insignificant as it is.
