Every dog has his/its day
Definition 1 of 1
Pro Tip 1/3Optimistic Assurance
The phrase often encourages people during tough times, suggesting good fortune is possible for anyone. 
Don't lose hope about finding a new job; every dog has his day.
Pro Tip 2/3Patience Suggested
Used to remind that success may take time, implying one's opportunity will come, eventually. 
She didn't make the team this year, but every dog has its day.
Pro Tip 3/3Not Literal
It's a metaphorical statement and does not involve real dogs; it's about people's success. 
Though he's an underdog in the competition, every dog has his day.