seal your fate, seal the deal, Strike a Deal

Novelist Ryotaro Shiba (1923-1996) once noted that "being able to compromise wisely" was a superior political ability. I believe "compromise" here means the same as "agreement." To strike a wise compromise, one must have the wisdom to draw concessions out of the negotiating partner, as well as the ability to bury one's differences for the broader perspective. Lacking either of these attributes, one cannot really hope to seal the deal.

Google and Creator of ‘Family Guy’ Strike a Deal

seal (MARK) Show phonetics
noun [C]
an official mark on a document, sometimes made with wax, which shows that it is legal or has been officially approved:
The lawyer stamped the certificate with her seal.

seal Show phonetics
verb [T]
to make an agreement more certain or to approve it formally:
The two leaders sealed their agreement with a handshake.

seal your fate
If an action, event or situation seals your fate, nothing can stop some unpleasant thing happening to you:
From the moment she stepped into the busy road her fate was sealed.

Decide what will become of one, as in The letter of rejection sealed his fate; he'd have to apply to other medical schools.

This term employs seal in the sense of "permanently fix or fasten something," a usage dating from the mid-1600s.