“Causa causans” is a Latin phrase that means “the causing cause” or “the cause that causes”
It is erroneously fashionable to talk about Karma vis-a-vis Destiny. More especially so, when one also, foolishly adds free-will to the karma (karmic action).
Karma or the karmic action and Destiny are as different as Day is from Night.
Night follows Day & vice versa. But, it is the light emitted by the Sun that creates the Day and absence of sunlight causes Night. The Day & Night per se, are not the causa causans of each other.
Like, you are free to switch on the lamp or light a candle etc. in the darkness; that’d still not change the fact that it is dark (night) . Similarly, you may exercise free-will. **But, that’ll not change your Destiny.**