A close talmid once observed Reb Shlomo Freifeld putting on his tefillin. After winding the tefillin shel yad around his arm, he stopped and closed his eyes, lost in thought. Only after a lengthy period of reflection did he continue with the tefillin shel rosh.
Later on, the talmid asked him why he had delayed placing the tefillin on his head.
Reb Shlomo related the story of the gemara in Brachos, in which one Amorah asked another one why he was smiling. “Ana tefillin kamanichna, I am putting on tefillin” was the reply.
Explained Reb Shlomo, “The act of putting on tefillin should fill the heart with joy. Today, I didn’t feel it, so I paused to reflect upon what was preventing me from feeling happy, and only once I felt the simcha shel mitzvah did I continue.” ~ The Life and Legacy of Rabbi Shlomo Freifeld zt”l