The Torah gives us (B'midbar 15:39) the cause and effect that are supposed to occur when we are in the proximity of a tzitzis:
'וְהָיָה לָכֶם לְצִיצִת וּרְאִיתֶם אֹתוֹ וּזְכַרְתֶּם אֶת כָּל מִצְוֹת ה
It should be tzitzis for you, and you should look at it and remember all of God's commandments.
We know that when the Torah says "remember" in a context like this it means "recite verbally", just like the commandment for kidush on shabas, which Chazal understood, and Rambam (29:1) said explicitly, must be accomplished through speaking:
מצות עשה מן התורה לקדש את יום השבת בדברים, שנאמר "זכור את יום השבת לקדשו"
[It is] a positive commandment from the Torah to sanctify the day of shabas with words, as it is said, "remember the day of shabas to sanctify it"
So when one sees a tzitzis one is obligated to recite all of the mitzvos. This would apply equally well to clothing worn by others as by oneself, since sometimes other people are even more aware of what you are wearing than you are, such as when you are wearing kil'ayim (10:29) and don't know it until it is spotted and ripped off of you in the street - "הרואה כלאים של תורה על חבירו אפילו היה מהלך בשוק קופץ לו וקורעו עליו מיד".
Now, that is a lot of mitzvos to recite - 613 by most counts although YמMV - each time a person sees a tzitzis, especially in areas where it is common to keep them visibly hanging out. And it becomes even more difficult to say them all when one wants l'kayem the added level of "אחרי מצותיך תרדוף נפשי", necessarily leaving the person out of breath by the time they even start.
- How can one fit in all that reciting of mitzvos and still have time left in the day?
- Does the list have to be the סמ"ג or would it be enough to say just the סמ"ק or even the סמ"ק?
- Is there a havinenu one can say instead?