Why i lose coins (simplified explanation)

1 : you receive shares , you mine the block and get the reward
2 : another ppl receive the same shares and mine the block too and get the reward too.
3 : when the blockchain is reorganized  the fastest miner keeps the reward and balances are updated (for the slowest miner, the block is orphaned)

This is due to latency and extreme fast time block ( during the launch).