Answer :
The time it would take from point a to point b and knowing which way to go by sea and navigating the sea.
Many factors actually did...
Ignorance of what may lie ahead
Sufficient amount of food and supplies
Possible native diseases and if where they travel might be dangerous
People willing(not many) because people had families to attend to caring for
Imprecise map depictions(not draw exactly correct)
HOPE THESE HELPED A LITTLE.
