Please don't beat yourself up! If I'm remembering correctly Rocky is about 8 months old? If so his adult fur is probably starting to come in... when that happens the mats seem to literally appear over night! Transition time is a nightmare. After he loses his puppy fur you'll get a better idea of how often you need to comb him to keep him mat free. You might want to start figuring out how to comb out a mat... cause this won't be his last one LOL. Keep a close eye on his arm pits... also known as mat magnets.
Just a couple hints for combing out mats.... first off saturate them with a good leave in conditioner and the wait 5 minutes before attacking. I usually start at the ends and work my way up towards the body. Hold the mat close to the skin to keep from pulling or hurting the dog while working on the mat. Chessie gets mats if she doesn't get brushed every 3rd day.... it takes patience and careful brushing/combing to work a mat out... stay calm and work carefully and you can get them out. One of the best things I did was train Chessie to lie down for grooming.... so she will just lay there and I can take as much time as I need to work.
Worse come to worse... there is no shame in cutting or shaving a mat out... especially if it saves your pup from extra stress.