The idiomatic expression "main hurdle" refers to a significant obstacle or challenge that must be overcome in order for something to happen, succeed or progress. Full definition
But there are two main hurdles for claiming the full 20 % deduction. (cpapracticeadvisor.com)
Industry challenges The two main hurdles facing the construction industry are labor and materials shortages. (nreionline.com)
Two main hurdles stand in the way of mass production and widespread consumer adoption of hydrogen «fuel cell» vehicles: the still high cost of producing fuel cells, and the lack of a hydrogen refueling network. (scientificamerican.com)