Each block in the blockchain contains a pointer to the previous block (block header). If multiple blocks reference certain block as their parent, only the one that is part of longest chain is accepted.
Suppose that the hash of the current blockchain tip (last block) is 'A'. Two miner concurrently works on new blocks (containing different transactions) referring to A as a parent. Is it necessary for the slower miner to reset his work when faster miner finishes his block (with hash 'B') and broadcasts it, because the next block has to reference 'B' instead of 'A' as a parent?
If this principle holds, does it mean that slower miners have to restart their work more frequently because they are outrun by faster miners who publish their blocks and so change the blockchain tip?