Why in the cond we must use true as the final condition? Why can't we use _?

[DevotionGeo]

@Ted

And :else also works in Elixir:

iex(6)> x = 11
11
iex(7)> cond do
...(7)>   x < 2  -> "x is less than 2"
...(7)>   x < 10 -> "x is less than 10"
...(7)>   :else  -> "x is greater than or equal to 10"
...(7)> end
"x is greater than or equal to 10"

Good point!
I like :else more than true.