What is 好高骛远 in English?
From Bai Du Zhi Dao:

好高骛远 (Hào gāo wù yuǎn) means: 


  比喻不切实际地追求过高过远的目标 (Bǐyù bù qiè shíjì dì zhuī qiú guò gāo guò yuǎn de
  mùbiāo.) : you unrealistically pursue goals that are too high and far.




To break down the phrase: 好高骛远

好 (Hào- 4th tone = likes/wants), so... 好高 (Hào gāo): likes/wants (things that are) high

骛 (wù): Greedy

远 (yuǎn): Far, Distant (So, 骛远 = over ambitious/over greedy)

To break that guy's response down:

不切实际 (bù qiè shíjì): Phrase to indicate impracticality of something

地 (dì): usually means "ground"... but here it follows an adverb. For example, 他慢慢地走过去 (he slowly walked over there). So, 慢慢 would be modifying the verb 追求 (zhuī qiú), so you use 地 (dì) between the adverb and the verb。 Like he "impractically pursued x": 他不切实际*地*追求x

追求 (zhuī qiú): to pursue something stubbornly. 

过高过远 (guò gāo guò yuǎn): 过 just means "pass over, too much, pass": so 过高 and 过远 just means too high and too far.

目标 (mùbiāo): Goal