Why did Tony Stark and Steve Rogers start clashing from their first encounter itself?

Definitely. Tony Stark and Steve Rogers are polar opposites. It can bring them together in some situations and bring them into conflict in others.

Steve was born poor and had to work hard for what he had, while Tony was born wealthy and had everything handed to him. Those surrounding Tony were more advanced and intelligent by nature unlike Steve, who constantly struggled to keep up. Both of them forged their own paths after losing their parents at a time when they most needed them. Steve lived in the real world while Tony chose to ignore it. Steve became a hero to serve others whereas Tony became a hero to atone for his own selfish faults. While Steve was the subject of experiments, Tony created his suit. Steve is cool and methodical, while Tony is brash and impetuous. Steve understands the value of having a team, but Tony is cocky, arrogant and thinks he can handle anything. Steve relies with in authorities, whilst Tony does not.

All of this results in their initial confrontations in The Avengers. They both want to serve people, but because of their opposing ideas, neither of them can be sure that the other is genuinely doing so. The fact of the matter is that once they are compelled to cooperate, both of them recognise the importance of the others and understand how it balances them out.

The intriguing thing is that, even today, their values continue to be diametrically opposed. Tony now feels that the authorities should control him and that he should plan ahead more to avoid repeating his failures as a result of Age of Ultron and Civil War. After Civil War and Winter Soldier, Steve started believing that he should trust himself over anybody else, as everyone has their selfish reasons. He became more aggressive within the law to do so.

However both of them proved each other wrong and,