Why always four?

Here is a puzzle to keep you busy in the New Year:

Choose any number

e.g. Seventy eight

Count the number of letters

Twelve

Count the number of letters

Six

Count the number of letters

Three

Count the number of letters

Five

Count the number of letters

Four

Count the number of letters

Four

Now we’re now stuck on four.

This always happens whatever number you set out with. Try it.

Why? Is there a proof for this?

Is it true in French, German, Spanish, etc.?