This is the 10030th most frequent Turkish word.
bakmasın
"Bakmasın" means "let him/her/it not look" or "he/she/it should not look."
Here, 'bakmasın' is used as a negated imperative or admonition form meaning 'let him/her not look'.
Arkasına bakmasın, ileriye odaklansın.
Do not let him/her look back, let him/her focus forward.
In this sentence, 'bakmasın' signifies 'not looking' and is directed to 'anyone' as a polite or indirect prohibition.
Kimse onun hatalarına bakmasın.
Do not let anyone look at his/her mistakes.
Here, 'bakmasınlar' indicates a plural-subject negated imperative form implying 'let them not look'.