The most challenging problems for a human being are to get the necessary skills, knowledge and behaviors that enable him/her to solve challenges, establish and lead a good productive life, which in some cases are different from the challenges of the human society, which are several and more complex.
For an individual man, the biggest challenge is to live as a good, selfless man in all sense. I think, in this highly competitive world, it is not an easy task for us to lead a successful life helping and without doing any harms to other people.
For the human kind, the biggest challenge is to live in harmony. At present we live in a compartmentalised world. We separate ourselves in to compartments due several vested interests like regional, religious, communal, political etc. So I think it is also very hard for us to break all these barriers and live as brothers and sisters in harmony and unison.
The question that you have asked is very intriguing. I would like to provide an answer based on Sufism:
The most difficult challenge for a human is to become complete. By complete I mean close to divinity. In persian 'انسانِ كامل', in arabic 'اَلإِنْسَانِ الكَامِلْ', read as: 'al-Insān al-Kāmil'. According to Rumi, Hafez and other Sufi scholars/philosophers, one needs to get rid of one's own veil. That is, everything that one has build in oneself against love. To quote Rumi: "Your task is not to seek love but to remove everything within yourself that you have build against it."
With regard to humanity, I would like to add the following poem from the wisdom of Saadi: "Of One Essence is the Human Race, Thusly has Creation put the Base. One Limb impacted is sufficient, For all Others to feel the Mace. The Unconcern'd with Others' Plight, Are but Brutes with Human Face."
Let us close my answer by another quote from Saadi: "Have patience. All things are difficult before they become easy."
In my humble opinion, the most difficult challenge for a human has been & will continue to be choosing between a good path or an evil path in dealing with the continuous daily situations. The evil path is tricky & may be full of attractions so the human has to be vigilant & tolerant in order to avoid falling into such trail which is disguised by instant superficial gains.
Personal answer: Self-Control and Respect for Others. If we can achieve these 2 think the world will be a better place / peaceful for all of us. We are not too late as we still have hope & we can do that if we want to. Wishing you and me all the best.
Life is a challenge & every human beings have to face it since his phase for his life to the childhood & onward..
It is a nature of challenge which every human being have in one or another day to face it initial as an observer to his line progress for his growth to meet the same with vigor & will power .
With this challenges may not be universal but in one or another way differ from individual to individual .Every man has an ambitious & desires for his growth & progressive way of his life in the line of his own development & it is the nature of development which may harness the challenge of the life .
It is the development of an individual which posses the problem of the challenge .As being observed that in quite good cases a person which its ambition ,will power & to move faster which his growth & the development such person who like to phase the challenges under the Belief that the sky is limit
Now-a-days, I am not going to respond or change my attitude based on the external events. Whatever is the external event, I m keeping myself in the same state. This question is not suitable for me
Human, in general, being a human is the big challenge
I would say 'balance'. I do believe that according to the pace of our day to day life and the unlimited number of tasks we have to deal with , it is very challenging to maintain a work & life balance and to preserve your calm and serenity. Regards.
For me perhaps the most difficult is the need to control myself when i see the others being very bad persons...
I often think that the actions are with those who practice them.
I believe that life has a broader meaning than just live ... we should be good to each other .... to some extent i believe in the three Christmas spirits .... the past, the present and the future ....
The interesting and disturbing is that I find persons that are not very human both in very intelligent and less intelligent people.... and i always thought that the intelligence as the ability to adapt to new situations, would help us to have more empathy and love for others, but in fact it is not so ...
In my opinion, the main and difficult challenge for a human being is their habits, Why? Because by defect we are selfish with everything we have around us. If we could share our knowledge and teach to the others we may work together, we could fix the troubles that we experiment everyday.
"Selfish in everything around us."...perhaps it is too much...I think that some people are selfish in doing "A" and others in "B", "C", etc....ie, in different fields...
But sharing our knowledge with others, by righting books, papers, converstion...is the way creativity leaves...because nothing is born of emptiness. Creativity is born of new applications on the already exist, and that is why we must share our knowledge with others.
I think I agree with Han's answer. the greatest challenge for a human is not to revert to that which we call uncivilised or animalistic tendencies in all aspects of our lives ... and that requires both self control and respect for others , e.g. in the face of adversity.