How these two meet
You two get on the road fast. Not as a figure of speech: the decision to go somewhere takes about a minute between you, and neither of you asks the other whether it is sensible.
The crack is that neither of you asks it afterwards either.
Mars wants the thing in front of it. Jupiter wants the size of the thing, where it goes, what it will have been. Both of those feel like appetite from the inside and they are not the same appetite.
So Aries commits and Sagittarius agrees, and six weeks in it turns out one of you was agreeing to the trip and the other to what the trip was going to mean.
Nobody lied. Jupiter genuinely was somewhere larger the whole time, and Mars genuinely was here.
What holds is that neither of you punishes the other for leaving. You both understand going. It is the coming back that has never had an agreed procedure.
For Aries, the work is asking once what this is for, before starting, and staying in the room for the whole answer.
For Sagittarius, the work is landing. Say the small, boring, actual version of the plan out loud, and let it be smaller than it was in your head.
The question
What are you running toward, and when did either of you last check?
One conscious action
one plan, said twice
Next time something gets decided in under a minute, stop and each say what you think was decided. Out loud, separately, before either of you hears the other.
The gap between the two versions is not the problem. It is the conversation you have been skipping for years, and it takes ninety seconds.
Mars is the faster of the two and Jupiter is the one that gets further, and you have never once had the argument about which of those you are doing.
When the two of you are already agreeing, who is left to ask where this is going?