You searched for: “guarantee
guarantee, guaranty
guarantee (gahr" uhn TEE) (noun)
A pledge that something is as represented and will be replaced if it doesn't meet specifications: The hand vacuum cleaner Shelby bought had a three-year guarantee.
guaranty (GAHR uhn tee) (noun)
A pledge by which a person commits himself/herself to the payment of another person's debt or obligation in the event of default: Cara's aunt signed the guaranty with Jerry when he borrowed money from the bank.

Celeste, if you will sign the guaranty for Trisha, she will guarantee that she will pay back all the money that she borrows from the bank. She promises!

(thinking that you can be successful in achieving an objective is a vital mental condition, but thinking that you can not do it is almost a guarantee that you will not be successful as indicated by Walter Wintle)