God forbid that I should boast except in the cross of our Lord Jesus Christ.
Why it is repeated
You may see people cross themselves at the mention of the Trinity, during blessings, at the Gospel, before receiving holy things, when entering or leaving the church, and during personal prayer. Repetition is part of formation. The Church repeats what the soul must remember.
How Copts usually make it
Copts commonly join three fingers together for the Holy Trinity and move from forehead to chest, then from left shoulder to right shoulder. The gesture places the mind, heart, strength, and whole person under the name of God.
The three fingers confess the Father, the Son, and the Holy Spirit. The movement over the body confesses that salvation is not only an idea held in the mind; Christ claims the whole person.
What the gesture teaches
The sign of the Cross is not a charm. It is a simple embodied confession: the Holy Trinity is worshiped, Christ crucified and risen is our salvation, and the whole person belongs to God. Repetition makes that confession natural.
This is why the faithful cross themselves at blessings, Gospel moments, prayers of the Trinity, and holy actions. The repeated gesture trains the person to remember the Cross at the exact moments when the Church is receiving grace, mercy, and truth.