为什么I want to have a try.要加to 而Let me have a try.不用加to

have a try 是一个动词词组，一个有关的动作的东西，而且有这个词组：want to do sth.

want to do
let是使役动词 后面不加to

want 后面要加不定式
所以要加 to
let 后面也要加不定式，但是let后的to 被省略了，你可以这么记。
读多了就记住了

want to do
let后面是省略to，属于三让之一嘛

want to do sth
want to 是固定搭配
let sb do sth
let 后要加省略to的不定式嘛

wang 后面加to 固定句型
let是使役动词 后面不加to

have是动词，前面要加to。
let sb. do sth. 是固定词组，比如let's go home

to have a try 是动词不定式短语做宾语补足语.
当谓语动词是Let,see, hear 的时候,做宾语补足语的不定式就要省略to：
I saw him go into the shop.
We heard the girl sing just now.

HAVE TO DO
LET SB. DO

want to do sth.