Count weapon damage once
Current attack usually counts for one face hit this turn. Durability matters for future turns, but lethal math starts with the attack you can make now.
Hero damage
Weapon and hero power lethal in Hearthstone
Hero damage is easy to forget because it sits outside the board and hand. Counting it as its own category prevents many one-off missed lethal turns.
Check hero power mana
A two-damage hero power is only real if the remaining mana allows it after your spells, minions, and weapon setup.
Watch attack replacement
Equipping a new weapon may replace the old one. Buffing hero attack may need to happen before the swing. Count the final attack state, not both.
Remember armor and prevention
Armor, immune effects, freeze, and taunt-like hero restrictions can stop the hero damage route even when the number looks high enough.
Simple habit
After board and hand, ask one extra question: what can my hero do this turn? That catches weapons, hero powers, and temporary attack buffs.