The ‘actual participation’ of the laity in the liturgy:

Occasionally I find myself having to say “Amen” at the end of prayers and in particular the Blessing as the People seem to think they shouldn’t say it without the priest leading them. In reality “Amen” is the People’s response as it means “So be it” - in other words the people are giving their assent to what the priest (or Bishop) has prayed for. The ‘Great Amen’ at the end of the Eucharistic Prayer is the most important example of when the People should say it and the priest shouldn’t. The priest has offered the prayer on behalf of the People and they signify their acceptance of what he has offered on their behalf by assenting to it with a heartfelt “Amen.” It is incongruous for the priest to say "Amen" as a response to what he has already prayed, and in doing so he would be usurping the People's actual participation.

Another important point to note is that the Eucharistic Prayer is prayed by the priest alone - it is a serious abuse for the people to join in the priest's parts of the Eucharistic Prayer, as they may only be said by a validly ordained priest. It is also an abuse of the people nearby who are trying to listen attentively and prayerfully. Some may ask “What then are we supposed to do?” The answer to which is to join in the people’s parts with sincere prayerfulness and devotion, and to listen attentively and prayerfully during the priest’s parts; and to say or sing the ‘Great Amen’ at the end of the Eucharistic Prayer with heartfelt conviction and thankfulness that Christ is now present with us under the veils of bread and wine upon the altar.