Reed's three biggest mistakes (chronological order):
1) Not addressing the chronic striker problem, window after window. In fact making it even worse by loaning out Gallagher, selling JRod and not bringing in any replacements.
2) Sacking Puel, in essence making him the scapegoat for 1) and our lack of cover with the CB situation (VVD injured and Fonte off).
3) Not sacking the current clown months ago.
Plenty of other mistakes too (Fonte fiasco, Toby fiasco, not addressing the goalkeeper situation, etc.), but those the biggies, and why we are in the current mess. 1) and 3) are totally unforgivable. 2) can also be blamed on the players who helped force Puel out.
Note I don't blame him for hiring the clown, since at the time it wasn't obvious what a total disaster he'd be. But there's no excuse for not firing him months ago, when everyone and their dog knew he was a thick, clueless, buffoon.