Plan formularies change every year. Premiums change every year. Networks change every year. The drug your plan covered as Tier 1 ($5/month) last year might be Tier 4 ($95/month) this year. Your specialist may have left the network. Your monthly premium may have jumped 15%.
The Annual Notice of Change (ANOC) document your plan mails you every September lists everything that's changing. Most beneficiaries don't read it — it's 30+ pages of fine print. So the changes blow past unnoticed, and you wake up in February realizing you're paying $200 more per month than you should.
The fix is a 30-minute October ritual. That's it. Run YOUR drug list against ALL Part D plans in your zip. Compare your current MA plan to alternatives. Check whether a different Medigap carrier is cheaper for the same Plan G. If a different plan saves $100+/year, switch. Old plan auto-disenrolls when new one starts.
Most retirees save $400-$1,000/year doing this. Over a 25-year retirement, that's $10,000-$25,000 of pure waste eliminated. The only reason most people don't do it: no deadline forces them to.