Q. I have always wondered. What is the Torah’s constant prevalent correct attitude. Should a person always feel besimcha, happy and content? Or should he constantly fear Hashem and be worried of the sins he has committed? You can’t be both at the same time.

A. Horav Yechezkel Levinshtein zt”l (Ohr Yechezkel 7: p. 381-386) maintains that the most important character trait that one should possess is serving Hashem with joy and happiness, as the posuk in our parsha clearly states that the reason to the dreadful tochacah is because you did not serve Hashem with happiness and with gladness of heart, when you had an abundance of everything. (Devarim 28: 47). He writes that the cause of all transgressions and evildoing resides in the desperation and depression people feel and in their lack of hope and joy in the future.
It is in that sense that we are to transform all negative thoughts and feelings of despair and sadness into the joy and happiness born from recognizing the constant great favors and kindness that Hashem grants to us, and thus return to Him.
On question 1729 in regards to the mitzva of learning Torah, we quoted Horav Shlomo Miller Shlit’a; “The Rov also advises to take into account to learn what is the most enjoyable and gratifying learning. He points out that if the learning is subject only to hardship and mesirus nefesh, it is unlikely to be maintained, continued or remembered. It has to be done also with great simcha and joy.”
On question 1138 in regards to someone that suffers, that our sages say that Hashem suffers with him, as it says; I’m with him in his trouble. “Is it then correct to say that a person should avoid suffering so Hashem will not suffer too? Or should one feel good, be happy and enjoy pleasant things, so Hashem will enjoy with him?”
“Horav Shlomo Miller’s Shlit”a opinion is that in principle you are correct, as Hashem is our Father, loves us with great love and only wishes only our benefit. However, sometimes our suffering and our distress are also part and parcel of that eventual well being. They may be either part of the kaparah and redemption processs, necessary to gain total forgiveness (similar to fasting), or they may be a nissayon or test that brings us to higher spiritual levels.
It goes without saying, that accepting the yissurim and their pain with simcha, love and happiness, (mekabel yisurim beahavah), thus turning them into an acceptable and even pleasant experience, would bring joy to Hashem.”
See also question 1437 in regards to the mitzva of simcha in Rosh Hashana, the Rov mentioned “that the simcha should be seen as “gilu bereada” (Tehilim 2: 11) or rejoice, while trembling.”

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a