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Ex 29:38
38 And it shall be upon Aaron's forehead, and Aaron shall bear the iniquity committed in the holy things, which the children of Israel shall hallow, even in all their holy gifts; and it shall be always upon his forehead, that they may be accepted before the LORD.
Reb Yehuda holds "always" /Tamid means that while he wears it he must constantly be cognizant of its presence and its kedusha. Reb Shimon holds it means that the Tzitz brings Ratzon - appeasement of the Ribono shel Olam" -constantly, even if it is not being worn at that moment.
The Gemara at the end of our daf says that "if we learn like Reb Yehuda, then if the Tzitz, which has the written name of Hashem only once, mandates constant respectful awareness, how much more so this is true for Tefillin which have Hashem's name written twenty one times."
Which leads us to examine the relationship between the two and the influence of "hesech hadaas" prevents us from wearing tefillin all day.