Herb, a tennis player, has been struggling to develop a more consistent serve. He made the following remark to his partner during the second set of a recent match: "I feel like I'm making progress. I haven't double-faulted once today." He then served two double-faults, which caused him to say, "Every time I say I haven't double-faulted, I immediately start to." Herb's perception may have been influenced by:

a. the present-aim standard of rationality.
b. unchecked the sunk cost effect.
c. unchecked the availability huerisitic.
d. unchecked regression to the mean.