In one sentence, why do more than 50% of new businesses fail in the first year?

I think they don't do the proper feasibility study because it could expensive and time consuming and they prefer to just benchmark with historical data of the markets and their competitors .
 

lack of market knowledge and field work.

Errors always produce the first experiment because it is balanced to some extent to the lack of expertise and experience

A business fails when its owner does not know what he is doing.
This a simple yet profound answer.

Partly because many fail the facility including the erroneous study of the target sector in terms of the volume of demand and purchasing power of the target customers, and product design in terms of the purchasing power of consumers and the quality of the product and its ability to satisfy the wishes and needs of customers.