Blocky saysUncle/stale blocks are valid blocks that lost the race to be the canonical next block.
When two miners produce a block at nearly the same time, the network temporarily forks; one branch wins and the other's block becomes stale (orphaned). Ethereum historically rewarded these as uncles to compensate miners and improve security. They show that "the chain" is really the heaviest/longest valid branch, and short reorgs are normal near the tip.
Power-ups you unlock
Two near-simultaneous blocks → temporary fork
Losing branch becomes stale/orphaned
Ethereum rewarded "uncles" historically
Canonical chain = heaviest valid branch
Double-Spend Dan attacks — common mistakes
Assuming the tip is instantly final
Treating a stale block as an attack
Forgetting short reorgs happen normally
Boss battleExplain why merchants wait for confirmations rather than trusting the latest block.
Example code
<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>two blocks at once → one wins, one goes stale
→ the tip can reorg → wait for confirmations</pre></body></html>