I’m assuming you mean big ideas like inventing the television and not two people thinking “hey let’s get pizza!” at the same time.

The rational: If you consider that at any point in time, the average person was facing the same problems as all the other average people, it is not too unreasonable to think that two people could think of the same solution since they were facing the same problem and likely had similar life experiences and education.

The cynical: We’re not as unique as we think we are.