Shavua Tov. The Talmud in Masechet Brachot mentions that both King David and Yakov Avinu worried that their own personal sins may have canceled the blessings already given by Hashem. The term used in Hebrew is, שמא יגרום החטא, that the sin caused the loss of the blessing.
The Rambam asks how it was possible for these two great Tzaddikim to ever feel that Hashem could possibly renege on a promise. After all, we identify a false prophet by seeing that his prophecy of “good” never came true.
The Rambam makes an interesting distinction between a blessing given by G-d on behalf of עם ישראל by way of a prophet, and a personal blessing given by G-d directly to a Tzaddik. In the first case, the positive prophecy given by way of a prophet, will, indeed, come true. But blessings given directly to people like King David and Yakov Avinu could be diminished because of sin.
We must never feel there are any guarantees in life and we must always strive to go higher and higher in our Avodat Hashem.