What is the difference between ばよかったです and べき?


What is the difference between ばよかったです and べき?

> あのバスに乗ればよかったです。  
>  I should have taken that bus.
>
> あのバスに乗るべきだった。  
>  I should have taken that bus.
>
> このバスに乗れるはずじゃなかった。  
>  I wasn’t supposed to get on this bus.
>
> 簡単なはずです。  
>  It should be easy.




ばよかった - "should have" in the sense "I wish I had" or "it would have been
better if I had"

べき - "should have" in the sense of "ought to". There is some expectation from
the outside, some other people, or society as a whole that you should better
do it.

はず - in contrast to べき, the expectation or assumption here comes from
yourself, prior experience etc.

