
If wishes were horses, beggars would/might ride
Imaginary Outcomes
The phrase emphasizes the difference between reality and desire, highlighting that wanting something doesn't ensure you'll get it. 
Practical Effort Needed
It suggests that actions are necessary to achieve goals, as opposed to just wishing for outcomes. 
Metaphoric Contrast
Beggars and riding symbolize the unlikely transformation from a poor state to one of prosperity just by wishing. 