If wishes were horses, beggars would/might ride
Definition 1 of 1
Pro Tip 1/3Imaginary Outcomes
The phrase emphasizes the difference between reality and desire, highlighting that wanting something doesn't ensure you'll get it. 
I'd love to skip exams, but if wishes were horses, beggars would ride.
Pro Tip 2/3Practical Effort Needed
It suggests that actions are necessary to achieve goals, as opposed to just wishing for outcomes. 
She wishes for a promotion, but if wishes were horses, beggars would ride.
Pro Tip 3/3Metaphoric Contrast
Beggars and riding symbolize the unlikely transformation from a poor state to one of prosperity just by wishing. 
He dreams of a big house, yet if wishes were horses, beggars would ride.