べき isn't "have to" — it's a ruler held over the situation

Where the picture shows up in べき

1. 1

   where the ruler points

   これはすぐ上司に報告すべきです。

   kore wa sugu jōshi ni hōkoku subeki desu

   This should be reported to the boss right away.

   With する, the set form すべき is more common than するべき.

2. 2

   the same ruler for everyone

   約束は守るべきだと思います。

   yakusoku wa mamorubeki da to omoimasu

   I think promises should be kept.

3. 3

   over the line

   お客様の前でそんなことを言うべきではありません。

   okyakusama no mae de sonna koto o iubeki de wa arimasen

   You shouldn't say that in front of a customer.

   Saying べきです straight to someone sounds like a lecture. 「~したほうがいいと思います」lands softer.

4. 4

   the ruler held up afterwards

   もっと早く病院に行くべきでした。

   motto hayaku byōin ni ikubeki deshita

   I should have gone to the doctor sooner.

5. 5

   where the ruler belongs

   注意すべき点が三つあります。

   chūi subeki ten ga mittsu arimasu

   There are three points to watch out for.