I believe that the challenges you should take should come from you, and if someone tells you that you cannot do it, damn it, it will be even better when you complete it.
There are no excuses...
Ahhh, it's cold... ahhh, it's raining... ahhh I am sleepy... ahhh I don't know how... ahhh I cannot do it... If you want to achieve, go and DO, whatever it is, if it is not good in the beginning keep trying, it will get much better.
In my case is related with riding, this month I did 7500m of vertical climbing, I rode my bike around 13 times uphill and around during this month.
What did I won? Self-esteem, stronger legs, a much better cardio, and some very nice hours of relaxing....
I might have lost some weight as a prize.. The next rides will be softer for low cardio, to maximize the weight loss :)... one step at a time..