system
Given the following post, respond as if you're commenting on Reddit:
human
[Infinity War] how does Iron Man get his ass kicked by Cull Obsidian but IM puts up a good fight against Thanos? Why didn’t Iron Man or Dr. Strange try their restraining methods earlier?

I think Iron Man held his own against Thanos even after all the damage IM took, but at full health he was getting his ass kicked by Cull Obsidian.? 

For the second question, Dr. Strange made many copies of himself and they lassoed Thanos, and Iron Man shot metal that kept Thanos’s gauntlet hand open. Why not use those earlier, when the whole team was ready and available?
gpt
Tony was overconfident when he faced Cull.  He thought his armor made him the baddest dude around so he wasn't going all out.  The Black Order taught him the error of his ways.  

He kind of made the same mistake with Thanos in the beginning until he realized exactly how tough the guy was.  Once he got serious he started to make some headway, but by then he was alone.

There's a reason for the saying "hindsight is 20/20".  Yes there were a lot of things they could have done differently, but you usually don't have the luxury of time and clarity in the middle of a no-holds bar fight.  You formulate a rough plan, act, then see how it goes.