To say for instance that something is good or too expensive FOR us, we use  /duì/ 

 /duì/ is a preposition of a confrontation with some phenomenon

When you want to say that something is too expensive FOR you or that smoking isn’t good FOR health, you use 对 /duì/.

对 /duì/ if FOR – but not in the sense that we have bought something for someone, but in the situations when we are describing attitude TO something or influence of one thing TO another.

Basically we take a phenomenon and put it OPPOSITE us (or someone or something else), we CONFRONT ourselves with it and say what the result of that confrontation is.

 

EXAMPLES

I am very satisfied with my new car.
我 对 我的 新的 汽车 很 满意。
Wǒ duì wǒde xīn de qìchē hěn mǎnyì.
He is nice to me.
他 对 我 很 好。
<Tā duì wǒ hěn hǎo.>
4am is too early for me.
早上 四 点 对 我 太 早。
<Zǎoshang sì diǎn duì wǒ tài zǎo.>
It is good for me to work in a global company.
在 跨国公司 工作 对 我 很 好。
Zài kuàguó gōngsī gōngzuò duì wǒ hěn hǎo.
He is nice to other people.
他 对 别人 很 好。
<Tā duì biérén hěn hǎo.>
I am very disapointed in you.
我 对 你 很 失望。
Wǒ duì nǐ hěn shīwàng.
It is good for me this way.
这样 对 我 很 好。
Zhèyàng duì wǒ hěn hǎo.
He is nice to me.
他 对 我 很 好。
<Tā duì wǒ hěn hǎo.>