Tefillin on the First Day of Shiva When Not Feeling Much Grief
Question
Answer
Even if one feels that they are not very grieved, and the main rule that tefillin is not worn on the first day is because it is the primary time of mourning, nevertheless, it is forbidden to wear tefillin as it is a disrespect to the tefillin and the mourning.
Source
Rashi in Tractate Sukkah, page 25a, writes: "And a mourner is not adorned, and when adorned, he shows that he is not mourning." Therefore, this reason applies even when he is not grieving, as he shows that he is not mourning.
And in Rashi, Tractate Ketubot, page 6: "Your crown is upon you (Ezekiel 24), and a mourner is covered in dust, and this is not an adornment for tefillin." This implies that it is a disrespect to the tefillin. Perhaps this reason does not apply when he is not covered in dust. However, Rashi's first reason is certainly more applicable when he is not grieving.
