Tzitzis are meant to be worn throughout the day as a constant reminder to observe the mitzvos of Hashem. There are various symbolisms found in the strings and knots which allude to the taryag mitzvos. For example, the five knots symbolize the chamisha Chumshei Torah. According to many poskim, there is a Torah commandment to gaze at the tzitzis and remind oneself of the mitzvos. Minimally, a person should look at the tzitzis when he wraps himself in his tallis koton. One should look at his tzitzis throughout the day, especially during moments of weakness when he feels himself succumbing to his yetzer hora.
[שו"ע כד, א, ג ו־ה, ומשנ"ב ו; ביאורים ומוספים דרשו, 6 ;תוס' מנחות מג, ב]