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.

   You hold the ruler over the document on your desk and the arrow points straight at your boss's seat.

   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.

   The same single ruler laid in turn over each person's very different circumstances.

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.

   The words spoken in front of the customer stick out past the last mark on the ruler.

   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.

   The ruler held over a date already gone by, measuring how far off you were.

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.

   Three marks stamped on the document, exactly where the ruler needs to be laid.