It is hard to put one word as the best in the world. Every one have their own perspective. from me it is "Dedication" or "Devotion" can be the words which can lead to your goal. Mohamadreza Rezaei Ahvanooei
Tank you so much for your helpful answers Dear Dr Sahar Qazi ,Mohammad Mehdizadeh , Mushtaq Ahmad , Subid Ghimire , Edwin Chigozie Nwokorie , Sivanathan Sivaruban , Djaafar Zemali, Sujay Vikram Singh and Jumoke Soyemi .
Thank you so much for your helpful answers Dear Dr Oluwaseun A. Otekunrin ,Amir Al-Khafaji, Muhammad Tariq , Jelena Popovic-Djordjevic ,Nazia Asad and Adriana Denisa Manea .
Before looking at other answers my top three were God, Muhammad (SAW), and mother. Reading replies from other colleagues, I agree with most of the responses.
Thank you so much for your helpful answers Dear Dr Marwan Khaleel Yousif ,Sanjoy Datta ,Ahsan Siddiqui ,Hamid Reza Samadifard ,Paul Olusegun Bankole and Vishnu Kumar Gupta .