It has been said that ambition is necessary in order for people to achieve success. However, not all successful people are ambitious and so, whilst it is often true, it is not absolutely essential.
Admittedly, ambition is a major contributor to success. It seems self-evident that ambitious people are more likely to go out and achieve great things. The history books are full of such examples, including great leaders, scientists, and athletes. Achieving anything of great importance requires overcoming challenges and often adversity, and this is of course hard to do without a sense of ambition.
That said, there are other factors to consider, and these might render ambition unnecessary in some cases. If a person is naturally talented, they might achieve amazing things in life without any sense of ambition. Take someone with a gift for music, as an example. They might be so astoundingly skilled that they can learn music easily, then impress others to the extent that they become famous. For others, this might be less about natural talent than passion. In other words, they might learn music out of personal interest and then practise it for their own enjoyment, ultimately earning the respect of the musical community not through ambition but through enthusiasm for music as an art and for their own sense of enjoyment.
In conclusion, in most cases it is probably true that ambition is essential for success; however, there are other factors to consider. Many incredibly successful people have achieved great things in spite of a lack of ambition simply due to their talent.