I try to not let it bug me, and @Daniel1598 's advice is spot on. But even after 200+ stays, getting downgraded a star on any category still stings. Not as much as it once did, but I still take it to heart.
One guy not that long ago gave me 4 * on check-in. He hated the phone app and refused to use it, but didn't bother to tell me that at any point during booking or before arrival, nor did he communicate his his plans to arrive 2 hours before check-in. Had he done so, I might have made arrangements. I was in a classroom with first graders when he got here, so my phone was off, and I missed his many voice mails, only picking them up 1/2 hour before normal check-in time. When I got home, all four of the people in the party were unhappily standing on the sidewalk in front of my house! I was able to explain to the other 3 how it works, and they understood perfectly. It was a warm day, so I opened a cold bottle of good white wine, etc., poured them each a glass, and they were fine. Unfortunately, he was the one who reviewed me. He downgraded me on value and accuracy, too.