言yán过guò其qí实shí

Literal: words exceed the reality
Figurative: To overstate things, to exaggerate beyond the facts; to make something sound better or bigger than it really is.

Where does 言过其实 come from?

The phrase comes from Liu Bei's judgment of the officer Ma Su. Though Ma Su was reputed to be talented and spoke brilliantly about strategy, Liu Bei warned Zhuge Liang that Ma Su's words exceeded the reality (言过其实) and that he should not be given great responsibility. Zhuge Liang ignored the warning and later entrusted Ma Su with defending Jieting; Ma Su disobeyed his orders, lost the position, and wrecked the whole campaign. Zhuge Liang had to execute him, and Liu Bei's warning stood proven: Ma Su's dazzling talk had outrun his actual ability.

Source (出处): 《三国志》

How is 言过其实 used? Two examples

他tā说shuō自zì己jǐ一yī个gè星xīng期qī就jiù能néng学xué会huì，这zhè话huà太tài言yán过guò其qí实shí了le。
He says he can learn it in a week; that's overstating things way beyond the facts.
广guǎng告gào里lǐ的de效xiào果guǒ有yǒu点diǎn言yán过guò其qí实shí，真zhēn用yòng起qǐ来lái没méi那nà么me好hǎo。
The results in the ad exaggerate a bit beyond reality; when you actually use it, it isn't that good.

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