Durham finished fifth in 2024 in their first season back in the top-flight after seven years in Division Two.
With the additions of batters Emilio Gay and Will Rhodes and seamer Sam Conners, Bostock says the belief was that a squad good enough to compete for the title had been assembled.
Yet Durham were on the back foot immediately as they lost their first two games. They won two of their next four, but then did not win any of their last eight, culminating in the ignominious innings defeat at Headingley.
When the county was last relegated in 2016, it was on the back of financial issues, but now it is on a much more stable footing.
The challenge then is a cricketing one for Bostock and the rest of the management team, including director of cricket Marcus North and head coach Ryan Campbell, who signed a new contract last month, to get promoted at the first attempt.