The Greeks defeated the Persians because they had a good army of their own, not a hired one. They built ships, they had a good strategy for how to win. The skill and cunning of the Greeks also played an important role. All the cities of Greece joined forces, and it was easier for them to defeat the enemy. Well, the main thing is that they had a good commander, Themistocles, who led them to victory over the Persians.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.