That is the greatest challenge of all.

To me, however, the greatest challenge is not the matter/question of...but (the matter/question) of...

We should welcome both the opportunity and the challenge.

To do this, think of some success that you have had in the past. Remind yourself of how you have faced some challenges and dealt with them.

But we have had to wrestle with the big challenges and have come to some ideas of where the answers lie.