7.8Strong beats versus weak beats

A practical guideline:

Strong-beat melody notes are more likely to define the harmony.

In 4/4:

Beat 1 is especially strong.

Beat 3 is also structurally important.

Beats 2 and 4 are weaker.

Offbeats are weaker still.

So if melody is:

C D E D

and C lands on beat 1 while D is a quick passing note, you probably do not need:

C chord → D chord.

You can simply keep C harmony.