To the point that / so that (以至于 / 以致)

Structure Cause / process，以至(于) / 以致(于) + result

以至(于) (yǐzhì(yú)) and 以致(于) (yǐzhì(yú)) sound identical but are NOT interchangeable. 以至(于) marks a GRADATION or escalation reaching an extreme: 激动得说不出话，以至于流泪 = "so moved he couldn't speak, to the point of weeping". 以致 introduces a CONSEQUENCE, almost always NEGATIVE or unwanted, of a prior mistake: 太轻敌，以致惨败 = "he underestimated the enemy, so he suffered a crushing defeat". Rule of thumb: if the result is harm caused by the previous action, use 以致; if it is an intensification that climbs in degree, use 以至. Both are written register; the 于 is optional and adds formality.

Examples

他tā激jī动dòng得de说shuō不bù出chū话huà，以yǐ至zhì于yú流liú下xià了le眼yǎn泪lèi。
He was so moved he couldn't speak, to the point of shedding tears.
问wèn题tí越yuè积jī越yuè多duō，以yǐ至zhì于yú无wú法fǎ收shōu拾shi。
The problems piled up to the point where they became impossible to fix.
他tā太tài轻qīng敌dí，以yǐ致zhì一yī败bài涂tú地dì。
He so underestimated his opponent that he was utterly defeated.
准zhǔn备bèi工gōng作zuò不bù充chōng分fèn，以yǐ致zhì整zhěng个gè计jì划huà失shī败bài了le。
The preparations were inadequate, so the whole plan fell through.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.