[77a top] The Gemarah discusses conditions of documents based upon when the “sun comes out of its container” [ie: when the sun comes out].
Rashi [Vaikra]: When Avraham had his Bris, Hashem took the sun “out of its container” to make it extremely extra hot that day so guests would not disturb him, while he was in pain.
R’ Moshe Feinstein: Even though Moshe was not ‘missing out’ on Mitzvos (since people were not there to invite in), his entire essence was that of Chessed (unlimiting giving) and he was unable to act out his defining characteristic and desire. This caused him even more pain than the physical discomfort of his circumcision.
D-E-ep Thoughts (based on R’ Rosner): Instead of waiting for opportunities to arise, we should go out and seize the day! Of course we (should) feel bad about actual missed Mitzvah opportunities, but we should be striving for so much more. If no Mitzvah walks through our doorway, instead of sitting back on our comfortable couches, we should get up, go out, and find one!