Final answer:
The line that reflects the idea of pursuing one's dreams is "To dream is happiness! But let me just once see this clearly wholly; then I can go on dreaming till the thing falls."
Step-by-step explanation:
The line from Eugene O'Neill's Beyond the Horizon that reflects the idea of pursuing one's dreams is:
"To dream is happiness! But let me just once see this clearly wholly; then I can go on dreaming till the thing falls."
In this line, the character Venters expresses the belief that dreaming brings happiness and that he will continue to dream until he achieves his goals. This reflects the theme of pursuing one's dreams in the play.