There were several animals that ran faster than man and many were stronger and thus, the early people needed to be alert, quick and have lots of presence of mind. Many plants and its products like fruits, nuts, roots were also dangerous. In the early period, they did not have sharp tools. The hunting tools were made up of stone and bones.
So, it was not easy to hunt the animals which ran faster. Likewise, use of unknown plants and its products was not safe. Gradually, one by one they would have learnt about the safe and unsafe plants. So, the difficulties were how to hunt the animals and birds and selection of non-poisonous plants and its products.