Maybe self motivation may be the most important but external stimuli are also important. External motivation is mainly important for stimulating self-motivation, and herein lies its importance.

Most of those who were able to succeed in achieving great goals necessarily believed in themselves and in their ability to implement and reach, even if they were constantly frustrated.
Today I watched the final match of the Wimbledon women's professional tennis championship, and as usual, the Tunisian Anas Jaber lost, who always won us back to lose in the final match. This provides an example that self-motivation is important to win all matches but can backfire when self-confidence becomes excessive.