What does "hit me like a two-by-four" mean?

What does this sentence mean?

This observation hit me like a two-by-four

2×4:

Image courtesy of Wikipedia.

Edit: Wikipedia has since corrected itself that this is indeed a 2×6, but you get the idea.

Oh, and the sentence as a whole means that the observation was a big surprise or a great shock; an aha experience or a eureka moment; an eye-opener.

• From the source: “ The nominal size is 2 by 4 inches but the actual size is 1.5 by 3.5 in (38 by 89 mm)”
– F'x
Jan 20, 2011 at 9:47
• Though, an actual hit by an actual 2x4 is more of an eye-closer... ;-) Jan 20, 2011 at 10:47
• @Jasper: I agree, it looks more like a 2x6 to me (1.5 x 5.5 in) Jan 20, 2011 at 12:12

• Maybe not quite 2x4, but close enough ;) (This is supposed to be humourous, please don't vote it above the real answers!) Jan 20, 2011 at 9:59
• Isn't that a standard-issue cluebat? ;-) Jan 20, 2011 at 10:48

A two by four is a common format for a piece of wood:

A length of sawn wood of cross section 2 inches by 4 inches, most often employed as structural framing lumber (dimension or dimensional lumber).

"It hit me like a two-by-four" means that you've been hit pretty hard.

In this context, the author uses it as a simile to convey his state of shock after reading the analysis he quoted. He felt that it explained so well why Asians were often stereotyped as good in science and math that it stunned him.

He explains this further down the page:

I hadn't known about the 1965 Act, and its existence and the above analysis just instantly explained so much so well and without reference to Asians somehow being magically different

In other words, he was really surprised by the quality of the explanation.

"Two-by-four" is a standard size of wood used in the UK building trade.

So it means a piece of wood with sides of two inches and four inches.

This may have derived from the story about how to handle Mules. "First" (clobbering mule with 2x4), "you have to get their attention."

Expression comes from a very old joke: about a farmer with a stubbron mule who would not go forward or backward let alone respond to owners comand. So the old man picks up a 2x4 and smacks the mule right between the eyes. Then the mule responded to command. Onlookers were outraged that the man punished the animal harshly. The farmer explained that "first he had to get the mules attention". I suspect over the years people have become more sensitive to this type of 'animal abus jokes' and it has died a just death, the source of this saying , lost.

The British army used to clean rifles after firing with a piece of "two-by-four" rag. In an armoury rolls of rag and "pull throughs" were kept. To clean the barrel of a rifle, one cut the rag on a red line and put it through the loop at one end of a piece of cord; at the other end of the cord was a weight. Open the breach, drop in the weight like a plumb line, and pull the rag through the barrel.

I'm surprised I haven't found this meaning in the dictionary.

• I believe "hit" by a two-by-four does not refer to a "two-by-four" cleaning rag. Instead, the other answers (from 4 and 5 years ago) are correct: it refers to a two-by-four wooden board. May 18, 2022 at 23:59