Lucy Has So Much Impact On Natsu's Actions
Natsu is rough by nature, he's unbashed. He loves embracing new challenges, sparring with strong people. Strength matters to him, so he applies that to most situation rather than using his head first. Unlike Lucy and Wendy and sometimes Gray, he doesn't actively search for ways to sort out problems inoffensively. Fighting is a second nature to him, even more so when his friends are in question. Sometimes it's even a way of evaluation for him.
However, he puts his preferences aside for Lucy, and it matters.
Natsu hurts himself while trying to break Erigor's wind wall, and Lucy stops him. And he does stop. Instead of trying to harm himself anymore, he uses his wits and suggests a way out of the situtaion.
He wants revenge from Phantom Lord for doing horrible things to Fairy Tail, he's ready to fight them. But Lucy feels guilty and starts crying.
Natsu doesn't really understand why, because none's actually blaming her for the circumstances, except herself.
In the end, he puts his preferences aside for her, his anger subdues and he drops the idea of attacking Phantom Lord for the time being. Then takes her to the guild.
Here, Natsu is furious and ready to fight Faust and the Edolas army because they are treating his friends as an object, the lacrima is being chipped at.
The situation demands otherwise. So Lucy holds him back, doesn't let him lose his temper and helps regain his senses.
Yet again, Natsu puts his own emotions aside, because of Lucy. She's the one who makes him act reasonable. Though still frustrated, he stops and doesn't let his anger get the better of him.
And that's why :
Even when Natsu has no control over his feelings or actions, and is influenced by foreign power, he still recognises her and realises that Lucy is there. He stops only after she tells him that it's alright and over.