This is not considered a “failure”
When I check the Query Store DMVs, force_failure_count is 0. The last_force_failure_reason_desc is NONE.
Query Store didn’t fail to apply the narrow plan. Instead, it’s just deciding not to give it to me, now that I’ve forced that plan.
Seems kinda like an adolescent, doesn’t it?
The answer remains a bit of a mystery, but read on to see how Kendra troubleshoots this.