Against Weidman Anderson took way too much risk by overdoing his 'mind game'. By that I mean trying to dodge punches with head movements and hands down like he normally does but this time taking it way too far, and even pretending to be rocked. Essentially that's what got him knocked out.
Against Nick Diaz he was a bit cage rusty, coming back after 2 serious losses (1 KO and 1 shin broken in half), and fighting for the first time again after breaking his leg. He had to fight careful and as you say mind games wouldn't really work with Nick Diaz anyway.
EDIT: Whups, didn't mean to hijack this thread with Anderson-criticism. But the jist of what I'm saying is: His amazing head movement requires a conscious effort during a fight. He chooses to be defensive and evasive, rather than look for strikes and openings. The goal is to mess with his opponent's head until they get careless.
The downside being, careful and mentally strong opponents won't fall for it.
So, Spider head movement requires 1. consciously choosing to defend and dodge during a fight, 2. having an opponent who'd love to keep attacking and make you look good.
Yes, Anderson took the mind games too far. That's no explanation though. Writing it off to arrogance or carelessness doesn't make sense to me, he is a very calculating guy. His clowning wasn't a single mistake either, it was building up from the start of the fight, and he chose to keep doing it
even though he was not winning or in control of the fight. If you're beating a guy senseless, sure clown around, but if you're very evenly matched, clowning is a risk you choose to take in order to get an edge.
What I remember from Anderson-Weidman 1 was, Anderson started with pretty crazy footwork and upper body feints to confuse Weidman. But Weidman matched him, did not get baited and kept the pressure on. He made no mistakes, did not lose any exchanges. Anderson tried more funky techniques but did not win any exchanges with them, and Weidman just kept upping the pressure. At this point, with none of his smoke and mirrors working, and not feeling technically dominant in the standup, Anderson decides to clown as hard as possible, hopefully throwing Weidman off.
As for cage rust against Nick Diaz: Sure, maybe it played a factor. But when the GOAT who finishes every mortal with a crazy ninja trick doesn't perform one night, it's almost never accredited to his (world-class) opponents. "He's having an off night". Sorry Nick, it wasn't your footwork, your counter mind games or your pressure.
Sorry, but it just doesn't add up for me.. When people can't properly explain your successes (oh it's his superhuman reflexes, superhuman skills), and people can't explain your poor performances (oh his ring rust, bad nights, weird ambience) then your success is probably dependent on some factor that the spectators can't see. I'm convinced it's his mind games and provocation.