Deck这里指的是一副扑克牌，所以not playing with a full deck从字面解释就是在打一副缺牌的扑克。你想一副缺牌的扑克打得成牌吗? 当然不成，这就跟缺心眼的人办不成事儿一样。当然，not playing with a full deck这个习惯用语是用作比喻意义的，表示不是处于完好无缺的状态。

例句-1：Have you noticed that old man who sits on a park bench all day talking to himself? I overheard him today and he's just talking nonsense. I'm afraid the poor guy isn't playing with a full deck.

你有没有注意到整天坐在公园长凳上喃喃自语的那个老人?我偶然听到他说的全是毫无意义的废话，恐怕那可怜的家伙有点神志迷糊了。

2. Not having both oars in the water 举止笨拙、头脑不平衡

Oar是划船的桨。大多数非机动船都需要在水里划动双桨来推进。如果划船的人没把双桨都放下水中一齐划动，只有一把桨下水地乱划一气，那只船就会在原地团团转，进退不得，可见这个划船人有多笨拙。当然not having both oars in the water这个习惯用语现在不只是用来说笨拙的划船人，它的应用范围扩大了。

例句-2：Professor Blank is so absent-minded you think he doesn't have both oars in the water. But when you go to his class and listen to his lecture, you know why everybody says he's a genius in his field.

Blank教授老是那么心不在焉、丢三拉四的，你会觉得他头脑不正常。但是如果你去上他的课，听他的讲座的话，你会发现他在自己的学术领域内可真是才华出众。