What made planning a journey difficult in the early days of exploration

In the early days of exploration, there was little information about the world that lay beyond what you could see with your own eyes. If you were an explorer, it meant going out into the world not knowing what was out there, how long it would take to get there, or what dangers you could face. This made preparing for a trip very difficult. You couldn't really pack proper clothes for weather or climate change, or know exactly how much food you might need for your journey.