Great post!

I've played a little over 1,000 hours, but a lot of it has been casual mucking around and around 250 mapping or map testing. I've played maybe 250 competitive games with close to 160 wins, have ranked up to DMG before deranking after traveling for 3 months. The same stuff happens in DMG games as Silver games, it's just that DMG players have faster reactions and better aim and understand the game better. I'm not a great aimer or leading fragger or anything but I usually maintain a 1k/d.

Some of the things that I've learned

Lack of map knowledge is a big issue, especially for players who are used to playing on Dust2. I've played many games on Dust2 where Novas for MG1 will be leading fraggers against DMG or higher, yet on any other map will anchor.

Learn the maps you play on, memorizing the play from the CT and T side, so that you know the most common CT hiding areas, as well as rotations and how the Terrorists attack. For example, on Inferno, it's possible to completely smoke off and molotov the B site, and flash your way in, and plant, without ever being seen, let alone hearing it. The best T teams know how the CTs play, where they position themselves, where they rotate, how long it takes to rotate etc. Without knowing any of this you'll be regularly caught off guard.

Players often don't understand how the economy works, why it's important for the Terrorists to get plant the bomb (+$800), when you should save, why you should save, what happens when you die after the timer etc. So many games I've played where the Terrorists will force up 2nd round and buy AKs or Galils after getting a plant in the first round, but losing it. I played 1 game where a team wiped us first round, one guy got a 4k including a knife, bought an AWP, and they lost every round afterwards. Weapons matter as well, when you should be forcing, when you should eco and how.

The economy often makes or breaks a game, and it's most evident on Nuke. If the terrorists can break the CTs bank, they have an excellent chance of winning the map.

Too many players go rogue, or go yolo, and just charge into crossfires and get wiped out. Sometimes they'll die in the first 10 seconds through stupidity or no forethought. Sometimes you're just unlucky and you get picked at mid in rifle battle. It completely screws up the round for that team and almost always guarantees a loss, especially if it's a T pick.

Pro tactics don't work in MM, because players lack the knowledge and skills to execute.