about the ”glass half empty“, It spawned a zillion joke variants, but i don't get the jokes...
I was reading the "What if", and this came up to me:
When people say “glass half empty”, they usually mean something like a glass containing equal parts water and air:
Traditionally, the optimist sees the glass as half full while the pessimist sees it as half empty. This has spawned a zillion joke variants—e.g., the engineer sees a glass that’s twice as big as it needs to be, the surrealist sees a giraffe eating a necktie, etc.

everyone knows the "glass half empty", but can anyone tell me something about the jokes it spawned, actually, i've never heard one, this is the first time i know about it...

why is "the engineer sees a glass that’s twice as big as it needs to be" funny? as a Chinese, it confuses me lot,
hope someone can help me, thank you~~

Question

about the ”glass half empty“, It spawned a zillion joke variants, but i don't get the jokes...
I was reading the "What if", and this came up to me:
When people say “glass half empty”, they usually mean something like a glass containing equal parts water and air:
Traditionally, the optimist sees the glass as half full while the pessimist sees it as half empty. This has spawned a zillion joke variants—e.g., the engineer sees a glass that’s twice as big as it needs to be, the surrealist sees a giraffe eating a necktie, etc.

everyone knows the "glass half empty", but can anyone tell me something about the jokes it spawned, actually, i've never heard one, this is the first time i know about it...

why is "the engineer sees a glass that’s twice as big as it needs to be" funny? as a Chinese, it confuses me lot, 
hope someone can help me, thank you~~

Answer

Humor is very subjective. I'll explain the two jokes you used: the engineer and the surrealist.

Because engineering is a very exact science (small mistakes can cause huge problems), the joke is that the glass is too big for the amount of water in it. In other words, if the glass is only half full, then the glass was made incorrectly. It should only be big enough to fit the amount of water that is in it. Personally, I don't think these jokes are funny even though I do understand them.

Now, the other one. Surrealism is an art form. In surrealism, the whole purpose is that NOTHING should make any sort of logical sense. Salvador Dali pioneered surrealism, and the giraffe portion of the joke definitely references his surrealist paintings (they usually have animals in them). Anyone who truly understands surrealism would know that referencing Dali's work by saying "giraffe" actually makes it NOT surreal. That joke fails.

Jokes are really hard to explain, and I don't even think those two are funny. I hope that helps, but I'll clarify anything you need me to because I know those explanations are hard to understand.

Answer

工程师看到一个两倍大的杯子时，会很郁闷，准确地装一半水是很困难的事情，一滴也不能多，一滴也不能少，太难了，郁闷啊^_^