Why do I need to change what I do successfully in my own country?
You may be the most successful business negotiator or team leader in your own company or country but do you know how to be polite, what is socially correct behaviour, what it is acceptable or considered offensive to talk about, how to meet, greet and present things in a different country? If you get it wrong, you will likely lose their trust, goodwill and future opportunities. If you appear rude, vulgar or disrespectful do you really think you are going to succeed? Just think of the equivalent 'bad behaviour' from a foreigner in your country - would it inspire you to want to work with them? It isn't always 'the best deal' that wins the contract.
Why are values and beliefs so important?
As an example think of the generally accepted differences between Americans, British, Japanese and French... Americans are meant to be all for money, British for good manners and fair play, Japanese for doing things collectively and extreme politeness, French for prioritising family over work. OK, this is a generalisation, caricature for each but based on elements of fact. So, if you treat them all the same, what happens? You offend all of them to a greater or lesser degree. If you want to be made welcome and have a good chance of succeeding you MUST accept and adapt to their values to be able to create and develop a good, loyal working relationship.