After finding the nonce, the typical miner broadcasts it as soon as possible so that other miners are aware that a block was found.
Those miners will validate the block for themselves before accepting it into their own chain, and then broadcast the block once more.
By broadcasting the block first, other miners will abandon their previous blocks and start to mine on this new longest chain.
At least, that’s the hope: there’s the possibility that someone else broadcasted a block before you that you haven’t yet seen! Only if your block makes its way into the longest chain will you reap the rewards.
So how do we ensure that happens? Well, we can’t! All we can do is hope that we got lucky.
That’s all Proof-of-Work really is at its base, a random lottery.