Room temperature IQ play by my partner

Well the title says it all. My partner and I collectively bid 10, while opposing team bid 1 and a nil. I understand if there’s 3-4 floating books out there left unaccounted for as wiggle room to deliberately set our opponent’s nil, but when you’re talking a double-digit bid and hardly no room at all for careless bad plays, I can’t imagine the thought process behind cutting my Ace of Diamonds with a King of Spades (if you see my previous post in this thread this exact same situation happened to me when my partner and I bid a full 13). In the end, we ended up setting our opponent’s nil on a 10 of spades, I proceeded to then choke out our nil opponent’s Queen of Spades; something that could’ve drastically altered the outcome of our bid given my partner carelessly threw the King of Spades earlier. In the end I managed to achieve 1 extra book to account for my partner’s not winning the 5 books they said they could win.