People still to this day doesn't get that Tevez accepted to play second fiddle, or better said to play his "cyclical" full warrior version in order to gain a place in Man Utd.That full warrior version it's kind of cool, builds a great connection with the crowd in the pitch, but that isn't his best version (sadly he comitted this mistake time and again with the NT).
He did that in order to in his way present his respects (maybe the only time in his whole carreer, because he really wanted bad to be a Man Utd player) understanding his initial "loan" player role and respecting the already established big players in the team.
Once he delivered (more as pitbull than the real full blown Tevez), he wanted first team treatment, as simple as that.
Anyone that thinks (even hating the dude, understandable BTW), that he wasn't a full blown special world class player, it's absolutely wrong, he is the definition of anywhere, anyhow against anything.
The more well rounded, more spectacular (and even leader) City's Tevez didn't appeared all of a sudden, that IS HIM, like he was prior to Man Utd in Boca and Corinthinas and mostly later in his more mature (on every sense, even fitness) Juve days.
That's why he got so angry and stubborned when they didn't want to buy him fast and to add salt to the injury spend on Berba (that also could have been bought and play perfectly with Wayne and him). There is when that initial loaned "humble", easy going Carlos, went full (and more real) "show me the money" Carlos. Then played his cards a la Tevez, his management (Kia and cia) at the same time was quite obscure and very money oriented, maybe even more than him (that's saying sthg.).
All of this combined with him being a fella that for the good and bad never care about what anyone thinks (who else would have stayed that calm after that move Mancini pulled on him abd went playing golf and without even tryng to clean his image), ended really bad (sadly).
In this whole Man Utd afair, he certainly felt he wasn't respected in a way he thinks he deserved.
On a strict football sense, Man Utd in many ways lost the plot there, Tevez with his usal antics and ego didn't help, but Fergie's ego was always really huge too and things collapsed. A pity because that day a big part of that combination of a team with skill and more than tenacity, plain ferocity as identity, went away to never return no matter how well other forwards and players did later and the Club still feels that change.
Keeping CR was more than probably impossible, but keeping that pair of Rooney and Carlos could have been done, at least as a BET.
If Fergie or the Managers didn't feel that they could have a Boca, Corinthians, City or Juve version with them (or even acknowledge that existed that version), yet at least a bet on him when the players themselves like Rooney questioned the idea behind letting go CR and Tevez go.
