for the first time 用法.for the first time i felt that i had achieved something.

你好。不一定的。比如说：
1 She was in London for the first time last week ------一般过去时
2 John is here with us in China for the first time ------一般现在时
3 For the first time in many years, Mary has had a kiss with a boy much older than she is -----现在完成时

总之，for the first time 这个结构不能决定谓语的时态。

本句中，for the first time 时间状语对应的动词是felt, 一般过去时，并非完成时

从句中had achieved 用过去完成时，是因为动作发生在felt 前，过去的过去。

for the first time 常用一般过去时，意思是 第一次。
比如 I saw the picture for the first time.

而it is/was +第几次+从句， 从句则要用完成时

比如 It is the first time that I have come here.
It was the first time that i had come here.

for the first time i felt that i had achieved something.这句话没错!for the first time 没有时态限制.这句felt 指过去,had achieved 是先于felt 发生的,指“过去的过去”,当然用过去完成时也可用于其它时态,如：...

这里是过去时 从句是过去完成时