The endorsement count is equal to the number of feedback posts which
include an endorsement for a
#progress-log minus the number of feedback posts which
do not include endorsements.
Example: If one badge awarder has posted an endorsement and a second awarder has posted non-endorsing feedback, the endorsement count is 0 and the badge will not be awarded. If a third awarder adds an endorsement, the new endorsement count will be 1 resulting in the badge being awarded.
For more info on feedback & endorsement...
Refer to
#Request-Feedback