In masechet shevuot, 41b, the gemara discusses a case of a loan as follows (h/t dafyomi.co.il)
Levi lent Yehudah, and told him 'repay me in front of two witnesses who learn Halachah. Yehudah paid without witnesses, and the money was lost through Ones. They came in front of Rav Nachman.
Levi: I stipulated that the repayment must be in front of witnesses who learn Halachah. I took the money for a deposit until we would find such witnesses.
Rav Nachman: He gave the money for payment, and you accepted it without objection (this shows that you pardoned your stipulation);
i. If you want, fulfill your stipulation now in front of Rav Sheshes and myself. We learn Halachah! (This was a joke.)
According to Rashi, when Levi accepted money from Yehudah and there were no witnesses present, he had the intent that the money was NOT a repayment, but a separate loan from Yehudah for which he was now a shomer chinam. When it gets lost, Levi is not responsible and, because the original loan was not paid back, Levi is still owed the original sum.
Rashi points out that "devarim shehayu belibecha einam devarim" [things that were in your (Levi's) heart are not things].
Isn't that obvious? Yehudah never specified this payment as a loan. Levi never said he was accepting it as a loan and not repayment. Levi never said to Yehudah that he would guard the money.
All of this was only going on in the mind of Levi. What was his hava amina that this is a valid way to think and bind Yehudah to his understanding? The gemara's flip answer (and Rashi's dismissal of the question through a clear tenet) indicate to me that this was a non-starter question, so why does the gemara even list it? Shouldn't a question presented in the text have an presumption of reasonableness?
Or is there a potential for Levi's thought process to be binding on Yehudah? Is there halachic precedent for the intent of one party to impose itself on the reality of another? In terms of shevuot, the rabbis prevent this by saying explicitly that the conditions of an oath taking are not the internal ones the oath taker might have (as in the case of Rava's cane and others, on 29a) but had they not made this explicit, is there a halachic construct allowing Yehudah's action of repayment to be considered something else by Levi and have Levi's thinking be determinant?