i can't explain the meaning of this sentences "no wind in our sail"
This sentences in the song of selena gomez
"This is a modern fairy tale
No happy endings
No wind in our sails
But I can't imagine a life without
Breathless moments"

Question

i can't explain the meaning of this sentences "no wind in our sail" 
This sentences in the song of selena gomez 
"This is a modern fairy tale
No happy endings
No wind in our sails
But I can't imagine a life without
Breathless moments"

Answer

It is a metaphor, meaning there is no "energy" left; no motivation.

Answer

It comes from this idiom: "take the wind out of someone's sails", and it means to make someone feel less determined and motivated about sth. 
https://dictionary.cambridge.org/dictionary/english/take-the-wind-out-of-sb-s-sails