ר"א לעולם ימוד אדם את עצמו אם יכול לכוין את לבו יתפלל ואם לאו אל יתפלל.
Rabbi Eliezer says: A person should always check oneself: if he can concentrate his heart--he should pray; if not--he should not pray.
Rabbi Chiya said: All the days of my life, I never had kavana. One time I tried to have kavana and focus my attention and ended up wondering about who would meet the king first: a Persian leader or the exilarch.
Shmuel said: I count birds.Rabbi Buni the son of Chiya said: I count people.Rabbi Matnayah said: I am grateful to my head that it knows when I get to "modim" that it bows on its own.
תניא אבא בנימין אומר אין תפלה של אדם נשמעת אלא בבית הכנסת שנאמר (מלכים א ח, כח) לשמוע אל הרנה ואל התפלה" במקום רנה שם תהא תפלה ...ומנין לעשרה שמתפללין ששכינה עמהם שנאמר אלהים נצב בעדת אל
It is taught that Abba Beinyamin says: a person's prayer is only heard in synagogue, as it is written (1 Kings 8:28) "hear the calling and the prayer", in a place of calling out that is where tefillah resides...How do we know that when ten gather to pray that God's Presence/Shechina is with them? since it is written: "Holy One resides in the community of God"