It means that the activities that they do are just to bring the other person down (usually during campaigning)
The answer is money. It was believed that if they found a shorter way to Asia that they could access the trading market more easily and avoid middle-men and things like that. They could open companies there and trade for much less money and earn much more. However, he ended up in the Americas, not India.
A self evident truth is a truth that proves itself without need of further validation. In other words, it’s so obviously true only a fool or someone who’s willfully ignorant would contest it.
