The phrase 'numbers game' often refers metaphorically to importance of quantities in achieving success. In social media marketing, it's a numbers game - the more followers, the better the reach.
Pro Tip 2/3
Idiomatic Usage
The term is used idiomatically and may not refer to actual numbers or a game. Getting into college has become a numbers game with the increasing applicants.
Pro Tip 3/3
Uncertain Outcome
It implies a situation where hard work doesn't guarantee success, but increasing attempts might. Job hunting is a numbers game; send more applications to improve your chances.